Project: Alluxio (Runtime / Cloud Native Storage)
File: Install-Alluxio-Cluster-with-HA.md

layout: global title: Install Alluxio Cluster with HA An Alluxio cluster with High Availability (HA) is achieved by running multiple Alluxio master processes on different nodes in the system. One master is elected as the leading master which serves all workers and clients as the primary point of contact. The other masters act as standby masters and maintain the same file system state as the leading master by reading a shared journal. Standby masters do not serve any client or worker requests; however, if the leading master fails, one standby master will automatically be elected as the new leading master. Once the new leading master starts serving, Alluxio clients and workers proceed as usual. During the failover to a standby master, clients may experience brief delays or transient errors. The major challenges to achieving high-availability are maintaining a shared file system state across service restarts and maintaining consensus among masters about the identity of the leading master after failover. : Uses an internal replicated state machine based on the to both store the file system journal and run leader elections. This approach is introduced in Alluxio 2.0 and requires no dependency on external services. To deploy an Alluxio cluster, first the pre-compiled Alluxio binary file, extract the tarball and copy the extracted directory to all nodes (including nodes running masters and workers). Enable SSH login without password from all master nodes to all worker nodes. You can add a public SSH key for the host into `~/.ssh/authorized_keys`. See for more details. TCP traffic across all nodes is allowed. For basic functionality make sure RPC port (default :19998) is open on all nodes. Alluxio admins can create and edit the properties file `conf/alluxio-site.properties` to configure Alluxio masters or workers. If this file does not exist, it can be copied from the template file under `${ALLUXIO_HOME}/conf`: ```shell $ cp conf/alluxio-site.properties.template conf/alluxio-site.properties ``` Make sure that this file is distributed to `${ALLUXIO_HOME}/conf` on every Alluxio master and worker before starting the cluster. Restarting Alluxio processes is the safest way to ensure any configuration updates are applied. The minimal configuration to set up a HA cluster is to give the embedded journal addresses to all nodes inside the cluster. On each Alluxio node, copy the `conf/alluxio-site.properties` configuration file and add the following properties to the file: ```properties alluxio.master.hostname=<MASTER_HOSTNAME> # Only needed on master node alluxio.master.embedded.journal.addresses=<EMBEDDEDJOURNALADDRESS> ``` Explanation: The first property `alluxio.master.hostname=<MASTER_HOSTNAME>` is required on each master node to be its own externally visible hostname. This is required on each individual component of the master quorum to have its own address set. On worker nodes, this parameter will be ignored. Examples include `alluxio.master.hostname=1.2.3.4`, `alluxio.master.hostname=node1.a.com`. The second property `alluxio.master.embedded.journal.addresses` sets the sets of masters to participate Alluxio's internal leader election and determine the leading master. The default embedded journal port is `19200`. An example: `alluxio.master.embedded.journal.addresses=masterhostname1:19200,masterhostname2:19200,masterhostname3:19200` Note that embedded journal feature relies on which uses leader election based on the Raft protocol and has its own format for storing journal entries. Enabling embedded journal enables Alluxio's internal leader election. See for more details and alternative ways to set up HA cluster with internal leader election. Before Alluxio can be started for the first time, the Alluxio master journal and worker storage must be formatted. Formatting the journal will delete all metadata from Alluxio. Formatting the worker storage will delete all data from the configured Alluxio storage. However, the data in under storage will be

On all the Alluxio master nodes, list all the worker hostnames in the `conf/workers` file, and list all the masters in the `conf/masters` file. This will allow alluxio scripts to run operations on the cluster nodes. `init format` Alluxio cluster with the following command in one of the master nodes: ```shell $ ./bin/alluxio init format ``` In one of the master nodes, start the Alluxio cluster with the following command: ```shell $ ./bin/alluxio process start all ``` This will start Alluxio masters on all the nodes specified in `conf/masters`, and start the workers on all the nodes specified in `conf/workers`. To verify that Alluxio is running, you can visit the web UI of the leading master. To determine the leading master, run: ```shell $ ./bin/alluxio info report ``` Then, visit `http://<LEADER_HOSTNAME>:19999` to see the status page of the Alluxio leading master. Alluxio comes with a simple program that writes and reads sample files in Alluxio. Run the sample program with: ```shell $ ./bin/alluxio exec basicIOTest ``` When an application interacts with Alluxio in HA mode, the client must know about the connection information of Alluxio HA cluster, so that the client knows how to discover the Alluxio leading master. The following sections list three ways to specify the HA Alluxio service address on the client side. Users can pre-configure the service address of an Alluxio HA cluster in environment variables or site properties, and then connect to the service using an Alluxio URI such as `alluxio:///path`. For example, with Alluxio connection information in `core-site.xml` of Hadoop, Hadoop CLI can connect to the Alluxio cluster. ```shell $ hadoop fs -ls alluxio:///directory ``` Depending on the different approaches to achieve HA, different properties are required: If using embedded journal, set `alluxio.master.rpc.addresses`. ```properties alluxio.master.rpc.addresses=masterhostname1:19998,masterhostname2:19998,masterhostname3:19998 ``` Or specify the properties in Java option. For example, for Spark applications, add the following to `spark.executor.extraJavaOptions` and `spark.driver.extraJavaOptions`: ```properties -Dalluxio.master.rpc.addresses=masterhostname1:19998,masterhostname2:19998,masterhostname3:19998 ``` Users can also fully specify the HA cluster information in the URI to connect to an Alluxio HA cluster. Configuration derived from the HA authority takes precedence over all other forms of configuration, e.g. site properties or environment variables. When using embedded journal, use `alluxio://masterhostname1:19998, masterhostname2:19998,masterhostname3:19998/path` For many applications (e.g., Hadoop, Hive and Flink), you can use a comma as the delimiter for multiple addresses in the URI, like `alluxio://masterhostname1:19998,masterhostname2:19998,masterhostname3:19998/path`. For some other applications (e.g., Spark) where comma is not accepted inside a URL authority, you need to use semicolons as the delimiter for multiple addresses, like `alluxio://masterhostname1:19998;masterhostname2:19998;masterhostname3:19998`. Some frameworks may not accept either of these ways to connect to a highly available Alluxio HA cluster, so Alluxio also supports connecting to an Alluxio HA cluster via a logical name. In order to use logical names, the following configuration options need to be set in your environment variables or site properties. If you are using embedded journal, you need to configure the following configuration options and connect to the highly available alluxio node via `alluxio://ebj@[logical-name]` , for example `alluxio://ebj@my-alluxio-cluster`. alluxio.master.nameservices.[logical-name] unique identifier for each alluxio master node A comma-separated ID of the alluxio master node that determine all the alluxio master nodes in the cluster. For example, if you previously used `my-alluxio-cluster` as the logical name and wanted to use `master1,master2,master3` as individual IDs for each alluxio master, you configure this as such: ```properties alluxio.master.nameservices.my-alluxio-cluster=master1,master2,master3 ``` alluxio.master.rpc.address.[logical name]. [master node ID] RPC Address for each alluxio master node For each alluxio master node previously configured, set the full address of each alluxio master node, for example: ```properties alluxio.master.rpc.address.my-alluxio-cluster.master1=master1:19998 alluxio.master.rpc.address.my-alluxio-cluster.master2=master2:19998 alluxio.master.rpc.address.my-alluxio-cluster.master3=master3:19998 ``` Below are common operations to perform on an Alluxio cluster. To stop an Alluxio service, run: ```shell $

process stop all ``` This will stop all the processes on all nodes listed in `conf/workers` and `conf/masters`. You can stop just the masters and just the workers with the following commands: ```shell $ ./bin/alluxio process stop masters # stops all masters in conf/masters $ ./bin/alluxio process stop workers # stops all workers in conf/workers ``` If you do not want to use `ssh` to login to all the nodes and stop all the processes, you can run commands on each node individually to stop each component. For any node, you can stop a master or worker with: ```shell $ ./bin/alluxio process stop master # stops the local master $ ./bin/alluxio process stop worker # stops the local worker ``` Starting Alluxio is similar. If `conf/workers` and `conf/masters` are both populated, you can start the cluster with: ```shell $ ./bin/alluxio process start all ``` You can start just the masters and just the workers with the following commands: ```shell $ ./bin/alluxio process start masters # starts all masters in conf/masters $ ./bin/alluxio process start workers # starts all workers in conf/workers ``` If you do not want to use `ssh` to login to all the nodes and start all the processes, you can run commands on each node individually to start each component. For any node, you can start a master or worker with: ```shell $ ./bin/alluxio process start master # starts the local master $ ./bin/alluxio process start worker # starts the local worker ``` Adding a worker to an Alluxio cluster dynamically is as simple as starting a new Alluxio worker process, with the appropriate configuration. In most cases, the new worker's configuration should be the same as all the other workers' configuration. Run the following command on the new worker to add ```shell $ ./bin/alluxio process start worker # starts the local worker ``` Once the worker is started, it will register itself with the Alluxio leading master and become part of the Alluxio cluster. Removing a worker is as simple as stopping the worker process. ```shell $ ./bin/alluxio process stop worker # stops the local worker ``` Once the worker is stopped, and after a timeout on the master (configured by master parameter `alluxio.master.worker.timeout`), the master will consider the worker as "lost", and no longer consider it as part of the cluster. In order to add a master, the Alluxio cluster must operate in HA mode. If you are running the cluster as a single master cluster, you must configure it to be an HA cluster before having more than one master. See the for more information about adding and removing masters. In order to update the master-side configuration, you can first , update the `conf/alluxio-site.properties` file on master node, and then . Note that, this approach introduces downtime of the Alluxio service. Alternatively, one benefit of running Alluxio in HA mode is to use rolling restarts to minimize downtime when updating configurations: Update the master configuration on all the master nodes without restarting any master. Restart standby masters one by one (the cluster ). Elect a standby master as the leading master (tutorial ). Restart the old leading master that is now a standby master. Verify the configuration update. If you only need to update some local configuration for a worker (e.g., change the mount of storage capacity allocated to this worker or update the storage directory), the master node does not need to be stopped and restarted. Simply stop the desired worker, update the configuration (e.g., `conf/alluxio-site.properties`) file on that node, and then restart the process.