Project: Apache Hadoop (App Definition and Development / Database)
File: abfs.md

<! Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. See accompanying LICENSE file. --> <!-- MACRO{toc|fromDepth=1|toDepth=3} --> The `hadoop-azure` module provides support for the Azure Data Lake Storage Gen2 storage layer through the "abfs" connector To make it part of Apache Hadoop's default classpath, make sure that `HADOOPOPTIONALTOOLS` environment variable has `hadoop-azure` in the list, on every machine in the cluster ```bash export HADOOPOPTIONALTOOLS=hadoop-azure ``` You can set this locally in your `.profile`/`.bashrc`, but note it won't propagate to jobs running in-cluster. Supports reading and writing data stored in an Azure Blob Storage account. Fully Consistent* view of the storage across all clients. Can read data written through the `wasb:` connector. Presents a hierarchical file system view by implementing the standard Hadoop interface. Supports configuration of multiple Azure Blob Storage accounts. Can act as a source or destination of data in Hadoop MapReduce, Apache Hive, Apache Spark. Tested at scale on both Linux and Windows by Microsoft themselves. Can be used as a replacement for HDFS on Hadoop clusters deployed in Azure infrastructure. For details on ABFS, consult the following documents: ; MSDN Article from June 28, 2018. The Azure Storage data model presents 3 core concepts: Storage Account*: All access is done through a storage account. Container*: A container is a grouping of multiple blobs. A storage account may have multiple containers. In Hadoop, an entire file system hierarchy is stored in a single container. Blob*: A file of any type and size stored with the existing wasb connector The ABFS connector connects to classic containers, or those created with Hierarchical Namespaces. A key aspect of ADLS Gen 2 is its support for These are effectively directories and offer high performance rename and delete operations something which makes a significant improvement in performance in query engines writing data to, including MapReduce, Spark, Hive, as well as DistCp. This feature is only available if the container was created with "namespace" support. You enable namespace support when creating a new Storage Account, by checking the "Hierarchical Namespace" option in the Portal UI, or, when creating through the command line, using the option `--hierarchical-namespace true` You cannot enable Hierarchical Namespaces on an existing storage account Containers in a storage account with Hierarchical Namespaces are not (currently) readable through the `wasb:` connector. Some of the `az storage` command line commands fail too, for example: ```bash $ az storage container list --account-name abfswales1 Blob API is not yet supported for hierarchical namespace accounts. ErrorCode: BlobApiNotYetSupportedForHierarchicalNamespaceAccounts ``` The best documentation on getting started with Azure Datalake Gen2 with the abfs connector is It includes instructions to create it from , which can be installed on Windows, MacOS (via Homebrew) and Linux (apt or yum). The subcommand handles all storage commands, does the creation. Until the ADLS gen2 API support is finalized, you need to add an extension to the ADLS

```bash az extension add --name storage-preview ``` Check that all is well by verifying that the usage command includes `--hierarchical-namespace`: ``` $ az storage account usage: az storage account create [-h] [--verbose] [--debug] [--output {json,jsonc,table,tsv,yaml,none}] [--query JMESPATH] --resource-group RESOURCEGROUPNAME --name ACCOUNT_NAME [--sku {StandardLRS,StandardGRS,StandardRAGRS,StandardZRS,PremiumLRS,PremiumZRS}] [--location LOCATION] [--kind {Storage,StorageV2,BlobStorage,FileStorage,BlockBlobStorage}] [--tags [TAGS [TAGS ...]]] [--custom-domain CUSTOM_DOMAIN] [--encryption-services {blob,file,table,queue} [{blob,file,table,queue} ...]] [--access-tier {Hot,Cool}] [--https-only [{true,false}]] [--file-aad [{true,false}]] [--hierarchical-namespace [{true,false}]] [--bypass {None,Logging,Metrics,AzureServices} [{None,Logging,Metrics,AzureServices} ...]] [--default-action {Allow,Deny}] [--assign-identity] [--subscription _SUBSCRIPTION] ``` You can list locations from `az account list-locations`, which lists the name to refer to in the `--location` argument: ``` $ az account list-locations -o table DisplayName Latitude Longitude Name - -- East Asia 22.267 114.188 eastasia Southeast Asia 1.283 103.833 southeastasia Central US 41.5908 -93.6208 centralus East US 37.3719 -79.8164 eastus East US 2 36.6681 -78.3889 eastus2 West US 37.783 -122.417 westus North Central US 41.8819 -87.6278 northcentralus South Central US 29.4167 -98.5 southcentralus North Europe 53.3478 -6.2597 northeurope West Europe 52.3667 4.9 westeurope Japan West 34.6939 135.5022 japanwest Japan East 35.68 139.77 japaneast Brazil South -23.55 -46.633 brazilsouth Australia East -33.86 151.2094 australiaeast Australia Southeast -37.8136 144.9631 australiasoutheast South India 12.9822 80.1636 southindia Central India 18.5822 73.9197 centralindia West India 19.088 72.868 westindia Canada Central 43.653 -79.383 canadacentral Canada East 46.817 -71.217 canadaeast UK South 50.941 -0.799 uksouth UK West 53.427 -3.084 ukwest West Central US 40.890 -110.234 westcentralus West US 2 47.233 -119.852 westus2 Korea Central 37.5665 126.9780 koreacentral Korea South 35.1796 129.0756 koreasouth France Central 46.3772 2.3730 francecentral France South 43.8345 2.1972 francesouth Australia Central -35.3075 149.1244 australiacentral Australia Central 2 -35.3075 149.1244 australiacentral2 ``` Once a location has been chosen, create the account ```bash az storage account create --verbose \ --name abfswales1 \ --resource-group devteam2 \ --kind StorageV2 \ --hierarchical-namespace true \ --location ukwest \ --sku Standard_LRS \ --https-only true \ --encryption-services blob \ --access-tier Hot \ --tags owner=engineering \ --assign-identity \ --output jsonc ``` The output of the command is a JSON file, whose `primaryEndpoints` command includes the name of the store endpoint: ```json { "primaryEndpoints": { "blob": "https://abfswales1.blob.core.windows.net/", "dfs": "https://abfswales1.dfs.core.windows.net/", "file": "https://abfswales1.file.core.windows.net/", "queue": "https://abfswales1.queue.core.windows.net/", "table": "https://abfswales1.table.core.windows.net/", "web": "https://abfswales1.z35.web.core.windows.net/" } } ``` The `abfswales1.dfs.core.windows.net` account is the name by which the storage account will be referred to. Now ask for the connection string to the store, which contains the account key ```bash az storage account show-connection-string --name abfswales1 { "connectionString": "DefaultEndpointsProtocol=https;EndpointSuffix=core.windows.net;AccountName=abfswales1;AccountKey=ZGlkIHlvdSByZWFsbHkgdGhpbmsgSSB3YXMgZ29pbmcgdG8gcHV0IGEga2V5IGluIGhlcmU/IA==" } ``` You then need to add the access key to your `core-site.xml`, JCEKs file or use your cluster management tool to set it the option `fs.azure.account.key.STORAGE-ACCOUNT` to this value. ```XML <property> <name>fs.azure.account.key.abfswales1.dfs.core.windows.net</name> <value>ZGlkIHlvdSByZWFsbHkgdGhpbmsgSSB3YXMgZ29pbmcgdG8gcHV0IGEga2V5IGluIGhlcmU/IA==</value> </property> ``` Creation through the portal is covered in Key Steps Create a new Storage Account in a location which suits you. "Basics" Tab: select "StorageV2". "Advanced" Tab: enable "Hierarchical Namespace". You have now created your storage account. Next, get the key for authentication for using the default "Shared Key" authentication. Go to the Azure Portal. Select "Storage Accounts" Select the newly created storage account. In the list of settings, locate "Access Keys" and select that. Copy one of the access keys to the clipboard, add to the XML option, set in cluster management tools, Hadoop JCEKS file or KMS store. An Azure storage account can have multiple containers, each with the container name as the userinfo field of the URI used to reference it. For example, the container "container1" in the storage account just created will have the URL

You can create a new container through the ABFS connector, by setting the option `fs.azure.createRemoteFileSystemDuringInitialization` to `true`. Though the same is not supported when AuthType is SAS. If the container does not exist, an attempt to list it with `hadoop fs -ls` will fail ``` $ hadoop fs -ls abfs://container1@abfswales1.dfs.core.windows.net/ ls: `abfs://container1@abfswales1.dfs.core.windows.net/': No such file or directory ``` Enable remote FS creation and the second attempt succeeds, creating the container as it does so: ``` $ hadoop fs -D fs.azure.createRemoteFileSystemDuringInitialization=true \ -ls abfs://container1@abfswales1.dfs.core.windows.net/ ``` This is useful for creating accounts on the command line, especially before the `az storage` command supports hierarchical namespaces completely. You can use the Any configuration can be specified generally (or as the default when accessing all accounts) or can be tied to a specific account. For example, an OAuth identity can be configured for use regardless of which account is accessed with the property `fs.azure.account.oauth2.client.id` or you can configure an identity to be used only for a specific storage account with `fs.azure.account.oauth2.client.id.<account_name>.dfs.core.windows.net`. This is shown in the Authentication section. Authentication for ABFS is ultimately granted by . The concepts covered there are beyond the scope of this document to cover; developers are expected to have read and understood the concepts therein to take advantage of the different authentication mechanisms. What is covered here, briefly, is how to configure the ABFS client to authenticate in different deployment situations. The ABFS client can be deployed in different ways, with its authentication needs driven by them. With the storage account's authentication secret in the configuration: "Shared Key". Using OAuth 2.0 tokens of one form or another. Deployed in-Azure with the Azure VMs providing OAuth 2.0 tokens to the application, "Managed Instance". Using Shared Access Signature (SAS) tokens provided by a custom implementation of the SASTokenProvider interface. What can be changed is what secrets/credentials are used to authenticate the caller. The authentication mechanism is set in `fs.azure.account.auth.type` (or the account specific variant). The possible values are SharedKey, OAuth, Custom and SAS. For the various OAuth options use the config `fs.azure.account .oauth.provider.type`. Following are the implementations supported ClientCredsTokenProvider, UserPasswordTokenProvider, MsiTokenProvider and RefreshTokenBasedTokenProvider. An IllegalArgumentException is thrown if the specified provider type is not one of the supported. All secrets can be stored in JCEKS files. These are encrypted and password protected use them or a compatible Hadoop Key Management Store wherever possible The exponential retry policy used for the AAD token fetch retries can be tuned with the following configurations. `fs.azure.oauth.token.fetch.retry.max.retries`: Sets the maximum number of retries. Default value is 5. `fs.azure.oauth.token.fetch.retry.min.backoff.interval`: Minimum back-off interval. Added to the retry interval computed from delta backoff. By default this is set as 0. Set the interval in milli seconds. `fs.azure.oauth.token.fetch.retry.max.backoff.interval`: Maximum back-off interval. Default value is 60000 (sixty seconds). Set the interval in milli seconds. `fs.azure.oauth.token.fetch.retry.delta.backoff`: Back-off interval between retries. Multiples of this timespan are used for subsequent retry attempts . The default value is 2. This is the simplest authentication mechanism of account + password. The account name is inferred from the URL; the password, "key", retrieved from the XML/JCECKs configuration files. ```xml <property> <name>fs.azure.account.auth.type.abfswales1.dfs.core.windows.net</name> <value>SharedKey</value> <description> </description> </property> <property> <name>fs.azure.account.key.abfswales1.dfs.core.windows.net</name> <value>ZGlkIHlvdSByZWFsbHkgdGhpbmsgSSB3YXMgZ29pbmcgdG8gcHV0IGEga2V5IGluIGhlcmU/IA==</value> <description> The secret password. Never share these. </description> </property> ``` Note: The source of the account key can be changed through a custom key provider; one exists to execute a shell script to retrieve it. A custom key provider class can be provided with the config

If a key provider class is specified the same will be used to get account key. Otherwise the Simple key provider will be used which will use the key specified for the config `fs.azure.account.key`. To retrieve using shell script, specify the path to the script for the config `fs.azure.shellkeyprovider.script`. ShellDecryptionKeyProvider class use the script specified to retrieve the key. OAuth 2.0 credentials of (client id, client secret, endpoint) are provided in the configuration/JCEKS file. The specifics of this process is covered in ; the key names are slightly different here. ```xml <property> <name>fs.azure.account.auth.type</name> <value>OAuth</value> <description> Use OAuth authentication </description> </property> <property> <name>fs.azure.account.oauth.provider.type</name> <value>org.apache.hadoop.fs.azurebfs.oauth2.ClientCredsTokenProvider</value> <description> Use client credentials </description> </property> <property> <name>fs.azure.account.oauth2.client.endpoint</name> <value></value> <description> URL of OAuth endpoint </description> </property> <property> <name>fs.azure.account.oauth2.client.id</name> <value></value> <description> Client ID </description> </property> <property> <name>fs.azure.account.oauth2.client.secret</name> <value></value> <description> Secret </description> </property> ``` An OAuth 2.0 endpoint, username and password are provided in the configuration/JCEKS file. ```xml <property> <name>fs.azure.account.auth.type</name> <value>OAuth</value> <description> Use OAuth authentication </description> </property> <property> <name>fs.azure.account.oauth.provider.type</name> <value>org.apache.hadoop.fs.azurebfs.oauth2.UserPasswordTokenProvider</value> <description> Use user and password </description> </property> <property> <name>fs.azure.account.oauth2.client.endpoint</name> <value></value> <description> URL of OAuth 2.0 endpoint </description> </property> <property> <name>fs.azure.account.oauth2.user.name</name> <value></value> <description> username </description> </property> <property> <name>fs.azure.account.oauth2.user.password</name> <value></value> <description> password for account </description> </property> ``` With an existing Oauth 2.0 token, make a request of the Active Directory endpoint `https://login.microsoftonline.com/Common/oauth2/token` for this token to be refreshed. ```xml <property> <name>fs.azure.account.auth.type</name> <value>OAuth</value> <description> Use OAuth 2.0 authentication </description> </property> <property> <name>fs.azure.account.oauth.provider.type</name> <value>org.apache.hadoop.fs.azurebfs.oauth2.RefreshTokenBasedTokenProvider</value> <description> Use the Refresh Token Provider </description> </property> <property> <name>fs.azure.account.oauth2.refresh.token</name> <value></value> <description> Refresh token </description> </property> <property> <name>fs.azure.account.oauth2.refresh.endpoint</name> <value></value> <description> Refresh token endpoint </description> </property> <property> <name>fs.azure.account.oauth2.client.id</name> <value></value> <description> Optional Client ID </description> </property> ``` , formerly "Managed Service Identities". OAuth 2.0 tokens are issued by a special endpoint only accessible from the executing VM (`http://169.254.169.254/metadata/identity/oauth2/token`). The issued credentials can be used to authenticate. The Azure Portal/CLI is used to create the service identity. ```xml <property> <name>fs.azure.account.auth.type</name> <value>OAuth</value> <description> Use OAuth authentication </description> </property> <property> <name>fs.azure.account.oauth.provider.type</name> <value>org.apache.hadoop.fs.azurebfs.oauth2.MsiTokenProvider</value> <description> Use MSI for issuing OAuth tokens </description> </property> <property> <name>fs.azure.account.oauth2.msi.tenant</name> <value></value> <description> Optional MSI Tenant ID </description> </property> <property> <name>fs.azure.account.oauth2.msi.endpoint</name> <value></value> <description> MSI endpoint </description> </property> <property> <name>fs.azure.account.oauth2.client.id</name> <value></value> <description> Optional Client ID </description> </property> ``` A Custom OAuth 2.0 token provider supplies the ABFS connector with an OAuth 2.0 token when its `getAccessToken()` method is invoked. ```xml <property> <name>fs.azure.account.auth.type</name> <value>Custom</value> <description> Custom Authentication </description> </property> <property> <name>fs.azure.account.oauth.provider.type</name> <value></value> <description> classname of Custom Authentication Provider </description> </property> ``` The declared class must implement `org.apache.hadoop.fs.azurebfs.extensions.CustomTokenProviderAdaptee` and optionally `org.apache.hadoop.fs.azurebfs.extensions.BoundDTExtension`. The declared class also holds responsibility to implement retry logic while fetching access tokens. A delegation token provider supplies the ABFS connector with delegation tokens, helps renew and cancel the tokens by implementing the CustomDelegationTokenManager interface. ```xml <property> <name>fs.azure.enable.delegation.token</name> <value>true</value> <description>Make this true to use delegation token provider</description> </property> <property> <name>fs.azure.delegation.token.provider.type</name> <value>{fully-qualified-class-name-for-implementation-of-CustomDelegationTokenManager-interface}</value> </property> ``` In case delegation token is enabled, and the config `fs.azure.delegation.token .provider.type` is not provided then an IlleagalArgumentException is thrown. A Shared Access Signature (SAS) token provider supplies the ABFS connector with SAS tokens by implementing the SASTokenProvider interface. ```xml <property> <name>fs.azure.account.auth.type</name> <value>SAS</value> </property> <property> <name>fs.azure.sas.token.provider.type</name> <value>{fully-qualified-class-name-for-implementation-of-SASTokenProvider-interface}</value> </property> ``` The declared class must implement `org.apache.hadoop.fs.azurebfs.extensions.SASTokenProvider`. The connector uses the JVM proxy settings to control its proxy setup. See The for the options to set. As the connector uses HTTPS by default, the `https.proxyHost` and `https.proxyPort` options are those which must be

In MapReduce jobs, including distcp, the proxy options must be set in both the `mapreduce.map.java.opts` and `mapreduce.reduce.java.opts`. ```bash export DISTCPPROXYOPTS="-Dhttps.proxyHost=web-proxy.example.com -Dhttps.proxyPort=80" hadoop distcp \ -D mapreduce.map.java.opts="$DISTCPPROXYOPTS" \ -D mapreduce.reduce.java.opts="$DISTCPPROXYOPTS" \ -update -skipcrccheck -numListstatusThreads 40 \ hdfs://namenode:8020/users/alice abfs://backups@account.dfs.core.windows.net/users/alice ``` Without these settings, even though access to ADLS may work from the command line, `distcp` access can fail with network errors. As with other object stores, login secrets are valuable pieces of information. Organizations should have a process for safely sharing them. File last access time is not tracked. Extended attributes are not supported. File Checksums are not supported. The `Syncable` interfaces `hsync()` and `hflush()` operations are supported if `fs.azure.enable.flush` is set to true (default=true). With the Wasb connector, this limited the number of times either call could be made to 50,000 . If abfs has the a similar limit, then excessive use of sync/flush may cause problems. As with all Azure storage services, the Azure Datalake Gen 2 store offers a fully consistent view of the store, with complete Create, Read, Update, and Delete consistency for data and metadata. For containers with hierarchical namespaces, the scalability numbers are, in Big-O-notation, as follows: | Operation | Scalability | |--|-| | File Rename | `O(1)` | | File Delete | `O(1)` | | Directory Rename:| `O(1)` | | Directory Delete | `O(1)` | For non-namespace stores, the scalability becomes: | Operation | Scalability | |--|-| | File Rename | `O(1)` | | File Delete | `O(1)` | | Directory Rename:| `O(files)` | | Directory Delete | `O(files)` | That is: the more files there are, the slower directory operations get. Further reading: The ABFS connector supports a number of limited-private/unstable extension points for third-parties to integrate their authentication and authorization services into the ABFS client. `CustomDelegationTokenManager` : adds ability to issue Hadoop Delegation Tokens. `SASTokenProvider`: allows for custom provision of Azure Storage Shared Access Signature (SAS) tokens. `CustomTokenProviderAdaptee`: allows for custom provision of Azure OAuth tokens. `KeyProvider`. Consult the source in `org.apache.hadoop.fs.azurebfs.extensions` and all associated tests to see how to make use of these extension points. Warning These extension points are unstable. Consult the javadocs for `org.apache.hadoop.fs.azurebfs.constants.ConfigurationKeys`, `org.apache.hadoop.fs.azurebfs.constants.FileSystemConfigurations` and `org.apache.hadoop.fs.azurebfs.AbfsConfiguration` for the full list of configuration options and their default values. Config `fs.azure.client.correlationid` provides an option to correlate client requests using this client-provided identifier. This Id will be visible in Azure Storage Analytics logs in the `request-id-header` field. Reference: This config accepts a string which can be maximum of 72 characters and should contain alphanumeric characters and/or hyphens only. Defaults to empty string if input is invalid. Config `fs.azure.tracingcontext.format` provides an option to select the format of IDs included in the `request-id-header`. This config accepts a String value corresponding to the following enum options. `SINGLEIDFORMAT` : clientRequestId `ALLIDFORMAT` : all IDs (default) `TWOIDFORMAT` : clientCorrelationId:clientRequestId Config `fs.azure.enable.flush` provides an option to render ABFS flush APIs - HFlush() and HSync() to be no-op. By default, this config will be set to true. Both the APIs will ensure that data is persisted. Config `fs.azure.disable.outputstream.flush` provides an option to render OutputStream Flush() API to be a no-op in AbfsOutputStream. By default, this config will be set to true. Hflush() being the only documented API that can provide persistent data transfer, Flush() also attempting to persist buffered data will lead to performance issues. `fs.azure.account.expect.header.enabled`: This configuration parameter is used to specify whether you wish to send a expect 100 continue header with each append request or

It is configured to true by default. This flag configures the client to check with the Azure store before uploading a block of data from an output stream. This allows the client to throttle back gracefully -before actually attempting to upload the block. In experiments this provides significant throughput improvements under heavy load. For more information : https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Expect `fs.azure.account.operation.idle.timeout`: This value specifies the time after which the timer for the analyzer (read or write) should be paused until no new request is made again. The default value for the same is 60 seconds. Config `fs.azure.account.hns.enabled` provides an option to specify whether the storage account is HNS enabled or not. In case the config is not provided, a server call is made to check the same. Config `fs.azure.enable.check.access` needs to be set true to enable the AzureBlobFileSystem.access(). Requests failing due to server timeouts and network failures will be retried. PUT/POST operations are idempotent and need no specific handling except for Rename and Delete operations. Rename idempotency checks are made by ensuring the LastModifiedTime on destination is recent if source path is found to be non-existent on retry. Delete is considered to be idempotent by default if the target does not exist on retry. The group name which is part of FileStatus and AclStatus will be set the same as the username if the following config is set to true `fs.azure.skipUserGroupMetadataDuringInitialization`. The following configs are related to read and write operations. `fs.azure.io.retry.max.retries`: Sets the number of retries for IO operations. Currently this is used only for the server call retry logic. Used within `AbfsClient` class as part of the ExponentialRetryPolicy. The value should be greater than or equal to 0. `fs.azure.io.retry.min.backoff.interval`: Sets the minimum backoff interval for retries of IO operations. Currently this is used only for the server call retry logic. Used within `AbfsClient` class as part of the ExponentialRetryPolicy. This value indicates the smallest interval (in milliseconds) to wait before retrying an IO operation. The default value is 3000 (3 seconds). `fs.azure.io.retry.max.backoff.interval`: Sets the maximum backoff interval for retries of IO operations. Currently this is used only for the server call retry logic. Used within `AbfsClient` class as part of the ExponentialRetryPolicy. This value indicates the largest interval (in milliseconds) to wait before retrying an IO operation. The default value is 30000 (30 seconds). `fs.azure.io.retry.backoff.interval`: Sets the default backoff interval for retries of IO operations. Currently this is used only for the server call retry logic. Used within `AbfsClient` class as part of the ExponentialRetryPolicy. This value is used to compute a random delta between 80% and 120% of the specified value. This random delta is then multiplied by an exponent of the current IO retry number (i.e., the default is multiplied by `2^(retryNum - 1)`) and then contstrained within the range of [`fs.azure.io.retry.min.backoff.interval`, `fs.azure.io.retry.max.backoff.interval`] to determine the amount of time to wait before the next IO retry attempt. The default value is 3000 (3 seconds). `fs.azure.write.request.size`: To set the write buffer size. Specify the value in bytes. The value should be between 16384 to 104857600 both inclusive (16 KB to 100 MB). The default value will be 8388608 (8 MB). `fs.azure.read.request.size`: To set the read buffer size.Specify the value in bytes. The value should be between 16384 to 104857600 both inclusive (16 KB to 100 MB). The default value will be 4194304 (4 MB). `fs.azure.read.alwaysReadBufferSize`: Read request size configured by

will be honoured only when the reads done are in sequential pattern. When the read pattern is detected to be random, read size will be same as the buffer length provided by the calling process. This config when set to true will force random reads to also read in same request sizes as sequential reads. This is a means to have same read patterns as of ADLS Gen1, as it does not differentiate read patterns and always reads by the configured read request size. The default value for this config will be false, where reads for the provided buffer length is done when random read pattern is detected. `fs.azure.readaheadqueue.depth`: Sets the readahead queue depth in AbfsInputStream. In case the set value is negative the read ahead queue depth will be set as Runtime.getRuntime().availableProcessors(). By default the value will be 2. To disable readaheads, set this value to 0. If your workload is doing only random reads (non-sequential) or you are seeing throttling, you may try setting this value to 0. `fs.azure.read.readahead.blocksize`: To set the read buffer size for the read aheads. Specify the value in bytes. The value should be between 16384 to 104857600 both inclusive (16 KB to 100 MB). The default value will be 4194304 (4 MB). `fs.azure.buffered.pread.disable`: By default the positional read API will do a seek and read on input stream. This read will fill the buffer cache in AbfsInputStream and update the cursor positions. If this optimization is true it will skip usage of buffer and do a lock free REST call for reading from blob. This optimization is very much helpful for HBase kind of short random read over a shared AbfsInputStream instance. Note: This is not a config which can be set at cluster level. It can be used as an option on FutureDataInputStreamBuilder. See FileSystem#openFile(Path path) To run under limited memory situations configure the following. Especially when there are too many writes from the same process. `fs.azure.write.max.concurrent.requests`: To set the maximum concurrent write requests from an AbfsOutputStream instance to server at any point of time. Effectively this will be the threadpool size within the AbfsOutputStream instance. Set the value in between 1 to 8 both inclusive. `fs.azure.write.max.requests.to.queue`: To set the maximum write requests that can be queued. Memory consumption of AbfsOutputStream instance can be tuned with this config considering each queued request holds a buffer. Set the value 3 or 4 times the value set for s.azure.write.max.concurrent.requests. `fs.azure.analysis.period`: The time after which sleep duration is recomputed after analyzing metrics. The default value for the same is 10 seconds. `fs.azure.always.use.https`: Enforces to use HTTPS instead of HTTP when the flag is made true. Irrespective of the flag, `AbfsClient` will use HTTPS if the secure scheme (ABFSS) is used or OAuth is used for authentication. By default this will be set to true. `fs.azure.ssl.channel.mode`: Initializing DelegatingSSLSocketFactory with the specified SSL channel mode. Value should be of the enum DelegatingSSLSocketFactory.SSLChannelMode. The default value will be DelegatingSSLSocketFactory.SSLChannelMode.Default. Only one of the following two options can be configured. If config values of both types are set, ABFS driver will throw an exception. If using the global key type, ensure both pre-computed values are provided. A global encryption key can be configured by providing the following pre-computed

The key will be applied to any new files created post setting the configuration, and will be required in the requests to read ro modify the contents of the files. `fs.azure.encryption.encoded.client-provided-key`: The Base64 encoded version of the 256-bit encryption key. `fs.azure.encryption.encoded.client-provided-key-sha`: The Base64 encoded version of the SHA256 has of the 256-bit encryption key. ABFS driver supports an interface called `EncryptionContextProvider` that can be used as a plugin for clients to provide custom implementations for the encryption framework. This framework allows for an `encryptionContext` and an `encryptionKey` to be generated by the EncryptionContextProvider for a file to be created. The server keeps track of the encryptionContext for each file. To perform subsequent operations such as read on the encrypted file, ABFS driver will fetch the corresponding encryption key from the EncryptionContextProvider implementation by providing the encryptionContext string retrieved from a GetFileStatus request to the server. `fs.azure.encryption.context.provider.type`: The canonical name of the class implementing EncryptionContextProvider. `fs.azure.io.read.tolerate.concurrent.append`: When the config is made true, the If-Match header sent to the server for read calls will be set as * otherwise the same will be set with ETag. This is basically a mechanism in place to handle the reads with optimistic concurrency. Please refer the following links for further information. https://docs.microsoft.com/en-us/rest/api/storageservices/datalakestoragegen2/path/read https://azure.microsoft.com/de-de/blog/managing-concurrency-in-microsoft-azure-storage-2/ `fs.azure.list.max.results`: listStatus API fetches the FileStatus information from server in a page by page manner. The config is used to set the maxResults URI param which sets the page size(maximum results per call). The value should be > 0. By default, this will be 5000. Server has a maximum value for this parameter as 5000. So even if the config is above 5000 the response will only contain 5000 entries. Please refer the following link for further information. https://docs.microsoft.com/en-us/rest/api/storageservices/datalakestoragegen2/path/list `fs.azure.enable.checksum.validation`: When the config is set to true, Content-MD5 headers are sent to the server for read and append calls. This provides a way to verify the integrity of data during transport. This will have performance impact due to MD5 Hash re-computation on Client and Server side. Please refer to the Azure documentation for and APIs for more details ABFS driver has the capability to throttle read and write operations to achieve maximum throughput by minimizing errors. The errors occur when the account ingress or egress limits are exceeded and, the server-side throttles requests. Server-side throttling causes the retry policy to be used, but the retry policy sleeps for long periods of time causing the total ingress or egress throughput to be as much as 35% lower than optimal. The retry policy is also after the fact, in that it applies after a request fails. On the other hand, the client-side throttling implemented here happens before requests are made and sleeps just enough to minimize errors, allowing optimal ingress and/or egress throughput. By default the throttling mechanism is enabled in the driver. The same can be disabled by setting the config `fs.azure.enable.autothrottling` to false. `fs.azure.atomic.rename.key`: Directories for atomic rename support can be specified comma separated in this config. The driver prints the following warning log if the source of the rename belongs to one of the configured directories. "The atomic rename feature is not supported by the ABFS scheme ; however, rename, create and delete operations are atomic if Namespace is enabled for your Azure Storage account." The directories can be specified as comma separated values. By default the value is "/hbase" `fs.azure.infinite-lease.directories`: Directories for infinite lease support can be specified comma separated in this

By default, multiple clients will be able to write to the same file simultaneously. When writing to files contained within the directories specified in this config, the client will obtain a lease on the file that will prevent any other clients from writing to the file. When the output stream is closed, the lease will be released. To revoke a client's write access for a file, the AzureBlobFilesystem breakLease method may be called. If the client dies before the file can be closed and the lease released, breakLease will need to be called before another client will be able to write to the file. `fs.azure.lease.threads`: This is the size of the thread pool that will be used for lease operations for infinite lease directories. By default the value is 0, so it must be set to at least 1 to support infinite lease directories. If you set `fs.azure.abfs.latency.track` to `true`, the module starts tracking the performance metrics of ABFS HTTP traffic. To obtain these numbers on your machine or cluster, you will also need to enable debug logging for the `AbfsPerfTracker` class in your `log4j` config. A typical perf log line appears like: ``` h=KARMA t=2019-10-25T20:21:14.518Z a=abfstest01.dfs.core.windows.net c=abfs-testcontainer-84828169-6488-4a62-a875-1e674275a29f cr=delete ce=deletePath r=Succeeded l=32 ls=32 lc=1 s=200 e= ci=95121dae-70a8-4187-b067-614091034558 ri=97effdcf-201f-0097-2d71-8bae00000000 ct=0 st=0 rt=0 bs=0 br=0 m=DELETE u=https%3A%2F%2Fabfstest01.dfs.core.windows.net%2Ftestcontainer%2Ftest%3Ftimeout%3D90%26recursive%3Dtrue ``` The fields have the following definitions: `h`: host name `t`: time when this request was logged `a`: Azure storage account name `c`: container name `cr`: name of the caller method `ce`: name of the callee method `r`: result (Succeeded/Failed) `l`: latency (time spent in callee) `ls`: latency sum (aggregate time spent in caller; logged when there are multiple callees; logged with the last callee) `lc`: latency count (number of callees; logged when there are multiple callees; logged with the last callee) `s`: HTTP Status code `e`: Error code `ci`: client request ID `ri`: server request ID `ct`: connection time in milliseconds `st`: sending time in milliseconds `rt`: receiving time in milliseconds `bs`: bytes sent `br`: bytes received `m`: HTTP method (GET, PUT etc) `u`: Encoded HTTP URL Note that these performance numbers are also sent back to the ADLS Gen 2 API endpoints in the `x-ms-abfs-client-latency` HTTP headers in subsequent requests. Azure uses these settings to track their end-to-end latency. The problems associated with the connector usually come down to, in order Classpath. Network setup (proxy etc.). Authentication and Authorization. Anything else. If you log `org.apache.hadoop.fs.azurebfs.services` at `DEBUG` then you will see more details about any request which is failing. One useful tool for debugging connectivity is the . This validates the classpath, the settings, then tries to work with the filesystem. ```bash bin/hadoop jar cloudstore-0.1-SNAPSHOT.jar storediag abfs://container@account.dfs.core.windows.net/ ``` If the `storediag` command cannot work with an abfs store, nothing else is likely to. If the `storediag` store does successfully work, that does not guarantee that the classpath or configuration on the rest of the cluster is also going to work, especially in distributed applications. But it is at least a start. The `hadoop-azure` JAR is not on the classpah. ``` java.lang.RuntimeException: java.lang.ClassNotFoundException: Class org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem not found at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2625) at org.apache.hadoop.fs.FileSystem.getFileSystemClass(FileSystem.java:3290) at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:3322) at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:136) at org.apache.hadoop.fs.FileSystem$Cache.getInternal(FileSystem.java:3373) at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:3341) at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:491) at org.apache.hadoop.fs.Path.getFileSystem(Path.java:361) Caused by: java.lang.ClassNotFoundException: Class org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem not found at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:2529) at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2623)

16 more ``` Tip: if this is happening on the command line, you can turn on debug logging of the hadoop scripts: ```bash export HADOOPSHELLSCRIPT_DEBUG=true ``` If this is happening on an application running within the cluster, it means the cluster (somehow) needs to be configured so that the `hadoop-azure` module and dependencies are on the classpath of deployed applications. The `azure-storage` JAR is not on the classpath. The request wasn't authenticated while using the default shared-key authentication mechanism. ``` Operation failed: "Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature.", 403, HEAD, https://account.dfs.core.windows.net/container2?resource=filesystem&timeout=90 at org.apache.hadoop.fs.azurebfs.services.AbfsRestOperation.execute(AbfsRestOperation.java:135) at org.apache.hadoop.fs.azurebfs.services.AbfsClient.getFilesystemProperties(AbfsClient.java:209) at org.apache.hadoop.fs.azurebfs.AzureBlobFileSystemStore.getFilesystemProperties(AzureBlobFileSystemStore.java:259) at org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem.fileSystemExists(AzureBlobFileSystem.java:859) at org.apache.hadoop.fs.azurebfs.AzureBlobFileSystem.initialize(AzureBlobFileSystem.java:110) ``` Causes include: Your credentials are incorrect. Your shared secret has expired. in Azure, this happens automatically Your shared secret has been revoked. host/VM clock drift means that your client's clock is out of sync with the Azure servers the call is being rejected as it is either out of date (considered a replay) or from the future. Fix: Check your clocks, etc. There's no `fs.azure.account.key.` entry in your cluster configuration declaring the access key for the specific account, or you are using the wrong URL ``` $ hadoop fs -ls abfs://container@abfswales2.dfs.core.windows.net/ ls: Configuration property abfswales2.dfs.core.windows.net not found. ``` Make sure that the URL is correct Add the missing account key. There is no container of the given name. Either it has been mistyped or the container needs to be created. ``` $ hadoop fs -ls abfs://container@abfswales1.dfs.core.windows.net/ ls: `abfs://container@abfswales1.dfs.core.windows.net/': No such file or directory ``` Make sure that the URL is correct Create the container if needed it has a content-type `text/html`, `text/plain`, `application/xml` The OAuth authentication page didn't fail with an HTTP error code, but it didn't return JSON either ``` $ bin/hadoop fs -ls abfs://container@abfswales1.dfs.core.windows.net/ ... ls: HTTP Error 200; url='https://login.microsoftonline.com/02a07549-0a5f-4c91-9d76-53d172a638a2/oauth2/authorize' AADToken: HTTP connection to https://login.microsoftonline.com/02a07549-0a5f-4c91-9d76-53d172a638a2/oauth2/authorize failed for getting token from AzureAD. Unexpected response. Check configuration, URLs and proxy settings. proxies=none; requestId='dd9d526c-8b3d-4b3f-a193-0cf021938600'; contentType='text/html; charset=utf-8'; ``` Likely causes are configuration and networking: Authentication is failing, the caller is being served up the Azure Active Directory signon page for humans, even though it is a machine calling. The URL is wrong it is pointing at a web page unrelated to OAuth2.0 There's a proxy server in the way trying to return helpful instructions. When using , the files/directories in ADLS Gen2 by default will be owned by the service principal object id i.e. principal ID & submitting jobs as the local OS user 'user1' results in the above exception. The fix is to mimic the ownership to the local OS user, by adding the below properties to`core-site.xml`. ```xml <property> <name>fs.azure.identity.transformer.service.principal.id</name> <value>service principal object id</value> <description> An Azure Active Directory object ID (oid) used as the replacement for names contained in the list specified by fs.azure.identity.transformer.service.principal.substitution.list. Notice that instead of setting oid, you can also set $superuser here. </description> </property> <property> <name>fs.azure.identity.transformer.service.principal.substitution.list</name> <value>user1</value> <description> A comma separated list of names to be replaced with the service principal ID specified by fs.azure.identity.transformer.service.principal.id. This substitution occurs when setOwner, setAcl, modifyAclEntries, or removeAclEntries are invoked with identities contained in the substitution list. Notice that when in non-secure cluster, asterisk symbol * can be used to match all user/group. </description> </property> ``` Once the above properties are configured, `hdfs dfs -ls abfs://container1@abfswales1.dfs.core.windows.net/` shows the ADLS Gen2 files/directories are now owned by 'user1'. Following failures are known and expected to fail as of now. AzureBlobFileSystem.setXAttr() and AzureBlobFileSystem.getXAttr() will fail when attempted on root ("/") path with `Operation failed: "The request URI is invalid.", HTTP 400 Bad Request` See the relevant section in