Logstash

Logstash is a tool for managing events and logs. When used generically, the term encompasses a larger system of log collection, processing, storage and searching activities.
== Overview==
Various Wikimedia applications send log events to Logstash, which gathers the messages, converts them into JSON documents, and stores them in an OpenSearch cluster. Wikimedia uses OpenSearch Dashboards as a front-end client to filter and display messages from the OpenSearch cluster. These are the core components of our ELK stack, but we use additional components as well. Since we utilize more than the core ELK components, we refer to our stack as "ELK+'".
(OpenSearch and OpenSearch Dashboards were forked from Elasticsearch and Kibana when those became non-free, hence the name "ELK".)
===OpenSearch===
OpenSearch is a multi-node Lucene implementation.
===Logstash===
Logstash is a tool to collect, process, and forward events and log messages. Collection is accomplished via configurable input plugins including raw socket/packet communication, file tailing, and several message bus clients. Once an input plugin has collected data it can be processed by any number of filters which modify and annotate the event data. Finally logstash routes events to output plugins which can forward the events to a variety of external programs, local files, and several message bus implementations.
===OpenSearch Dashboards===
OpenSearch Dashboards is a browser-based analytics and search interface for OpenSearch.
=== Kafka ===
Apache Kafka is a distributed streaming system. In our ELK stack Kafka buffers the stream of log messages produced by rsyslog (on behalf of applications) for consumption by Logstash. Nothing should output logs to logstash directly, logs should always be sent by way of Kafka.
=== Rsyslog ===
Rsyslog is the "rocket-fast system for log processing". In our ELK stack rsyslog is used as the host "log agent". Rsyslog ingests log messages in various formats and from varying protocols, normalizes them and outputs to Kafka.
== OpenSearch quick intro ==
To learn how to use the dashboards at logstash.wikimedia.org, refer to OpenSearch Dashboards.
That's also where you can find how to access the Beta Cluster Logstash: OpenSearch Dashboards#Beta Cluster Logstash.
==Systems feeding into logstash==
See 2015-08 Tech talk slides
Writing new filters is easy.
=== Supported log shipping protocols & formats ("interfaces") ===
Support of logs shipped directly from application to Logstash has been deprecated.
Please see Logstash/Interface for details regarding long-term supported log shipping interfaces.
==== Kubernetes ====
Kubernetes hosted services are taken care of directly by the kubernetes infrastructure which ships via rsyslog into the logstash pipeline. All a kubernetes service needs to do is log in a JSON structured format (e.g. bunyan for nodejs services) to standard output/standard error. Note that some field names mind end up being a bit tricky. See also Logstash/Common Logging Schema for an effort to standardize on them.
===Systems not feeding into logstash===
*EventLogging (of program-defined events with schemas), despite its name, uses a different pipeline.
*Varnish logs of the billions of pageviews of WMF wikis would require a lot more hardware. Instead we use Kafka to feed web requests into Hadoop. A notable exception to this rule: varnish user-facing errors (HTTP status 500-599) are sent to logstash to make debugging easier.
*While most of MediaWiki logs go to Logstash (and mwlog files), a few channels go exclusively to mwlog files. You can check which ones, via $wmgMonologChannels in InitialiseSettings.php.
=== Writing & testing filters ===
When in the process of writing new logstash filters, take a look at what's existing already in puppet. Each filter must be tested to avoid regressions, we are using logstash filter verifier and existing tests can be found in the tests/ directory. To write tests or run existing tests you will need logstash-filter-verifier and logstash installed locally, or you can use docker/podman and the puppet repository:
# From the base dir of operations/puppet.
$ cd modules/profile/files/logstash/
# The Makefile recognizes if one of podman or docker is installed
# and then it uses it.
$ make test-local
/usr/bin/docker run --rm --workdir /src -v $(pwd):/src:Z -v $(pwd)/templates:/etc/logstash/templates:Z -v $(pwd)/filter_scripts:/etc/logstash/filter_scripts:Z --entrypoint make docker-registry.wikimedia.org/releng/logstash-filter-verifier:latest
logstash-filter-verifier --diff-command="diff -u --color=always" --sockets tests/ filters/*.conf
Use Unix domain sockets.
[...cut...]
Each filter has a corresponding test after its name in tests/. Within the test file the fields map lists the fields common to all tests and are used to trigger a specific filter's "if" conditions. The ignore key usually contains only @timestamp since that field is bound to change across invocations and can be safely ignored. The remainder of a test file is a list of testcases in the form of input/expected pairs. For "input" it is recommended to use yaml > to include verbatim JSON, whereas "expected" is usually yaml, although it can be also verbatim JSON if more convenient.
=== Getting logs from misc systems into logstash ===
Please see Logstash/Interface#Tailing Log Files.
==Production Logstash Architecture==
As of FY2019 Logstash infrastructure is owned by SRE. See also Logstash/SRE onboard for more information on how to migrate services/applications.
=== Architecture Diagram ===
=== Web interface ===
https://logstash.wikimedia.org
=== Authentication ===
Log into https://logstash.wikimedia.org/ with your Wikimedia Developer account (sometimes known as your "LDAP" account).
Access to Logstash is restricted to members that are in one of the these LDAP groups:
* wmf (for most Foundation staff),
* nda (for volunteers),
* ops (for SRE).
In the near future the access to Logstash will be moved to a dedicated group (this is not yet enabled):
* logstash-access
=== Configuration ===
The cluster contains two types of nodes, configured by Puppet.
* role::logging::opensearch::collector manages the Logstash "collector" instances. These run Logstash, an OpenSearch indexing node, and an Apache vhost serving OpenSearch Dashboards. The Apache vhosts perform LDAP-based authentication to restrict access to the potentially sensitive log information.
* role::logging::opensearch::data configures an OpenSearch data node providing storage for log data.
* role::kafka::logging configures a Kafka broker for producers to publish log data to and for Logstash to consume from. This is a buffering layer to absorb log spikes and queue log events when maintenance is being performed on the logging cluster.
===Hostnames===
In October of 2023, the Observability team decided to rename the Logstash cluster to better align with the role(s) of each host. The previous naming convention, regardless of role or configuration, assigned each node the hostname logstash. This legacy naming convention required operators to know by the host ID (1001, et. al.) the role, function, and class.
The new naming convention selection criteria included:
* a concise name that could be expanded as needed
* indicated the difference between stateful and stateless components
* did not specify the underlying technology deployed
* an incremental improvement over role assignment based on node id
The 10-2023 Logging Cluster Naming Convention:
* logging-hd - OpenSearch data node: HDD Class
* logging-sd - OpenSearch data node: SSD Class
* logging-fe - OpenSearch API (logs-api), OpenSearch Dashboards (kibana7), Logstash Collector node
=== Load Balancing and TLS ===
The "misc" Varnish cluster is being used to provide ssl termination and load balancing support for the Kibana application.
==Common Logging Schema==
Seeː Logstash/Common Logging Schema.
==API==
The Elasticsearch API is accessible at https://logs-api.svc.eqiad.wmnet or by SSH tunneling port 9200 from an opensearch node.
Note: The _search endpoint can only be used without a request body (see ). Use _msearch instead for complex queries that need a request body.
=== Extract data from Logstash (OpenSearch) with curl and jq ===
logstash-server:~$ cat search.sh
curl -XGET 'localhost:9200/_search?pretty&size=10000' -d '
{
 "query": {
 "query_string" : {
 "query" : "facility:19,local3 AND host:csw2-esams AND @timestamp:[2019-08-04T03:00 TO 2019-08-04T03:15] NOT program:mgd"
 }
 },
 "sort": ["@timestamp"]
} '
logstash-server:~$ bash search.sh | jq '.hits.hits[]._source | {timestamp,host,level,message}' | head -20
{
 "timestamp": "2019-08-04T03:00:00+00:00",
 "host": "csw2-esams",
 "level": "INFO",
 "message": " %-: (root) CMD (newsyslog)"
}
{
 "timestamp": "2019-08-04T03:00:00+00:00",
 "host": "csw2-esams",
 "level": "INFO",
 "message": " %-: (root) CMD ( /usr/libexec/atrun)"
}
{
 "timestamp": "2019-08-04T03:01:00+00:00",
 "host": "csw2-esams",
 "level": "INFO",
 "message": " %-: (root) CMD (adjkerntz -a)"
}
$ bash search.sh | jq -r '.hits.hits[]._source | {timestamp,host,level,program,message} | map(.) | @csv' > asw2-d2-eqiad-crash.csv
==Plugins==
Logstash plugins are fetched and compiled into a Debian package for distribution and installation on Logstash servers.
The plugin git repository is located at https://gerrit.wikimedia.org/r/#/admin/projects/operations/software/logstash/plugins
===Plugin build process===
The build can be run on the production builder host. See README for up-to-date build steps.
=====Deployment=====
* Add package to reprepro and install on the host normally.
:
==Gotchas==
===GELF transport===
Make sure logging events sent to the GELF input don't have a "type" or "_type" field set, or if set, that it contains the value "gelf". The gelf/Logstash config discards any events that have a different value set for "type" or "_type". The final "type" seen in OpenSearch/Dashboards will be take from the "facility" element of the original GELF packet. The application sending the log data to Logstash should set "facility" to a reasonably unique value that identifies your application.
==Documents==
== Troubleshooting ==
=== Kafka consumer lag ===
For a host of reasons it might happen that there's a buildup of messages on Kafka. For example:
; OpenSearch is refusing to index messages, thus Logstash can't consume properly from Kafka.
: The reason for index failure is usually conflicting fields, see also for a detailed discussion of the problem. The solution is to find what programs are generating the conflicts and drop them on Logstash accordingly, see also 
=== Using the dead letter queue ===
The DLQ can be found here. We save a maximum of two days of dead-letters to assist with debugging indexing issues.
== Operations ==
=== Configuration changes ===
After merging your configuration change Puppet will automatically restart Logstash. To force this to run:
 cumin -b1 -s60 'O:logging::opensearch::collector' 'run-puppet-agent -q'
==== Test a configuration snippet before merge ====
Copy your ready to merge snippet (eg. modules/profile/files/logstash/filter-syslog-network.conf) to a Logstash host.
Then run 
 sudo /usr/share/logstash/bin/logstash --config.test_and_exit -f <myfile>
It should return "Configuration OK".
=== Indexing errors ===
Have a look at the Dead Letter Queue Dashboard. The original message that caused the error is in the log.original field.
We're alerting on errors that Logstash gets from OpenSearch whenever there's an "indexing conflict" between fields of the same index (see also ). The reason usually is because two applications send logs with the same field name but two different types, e.g. response will be sent as a string in one case but as nested object in another. is a good example of this, where different parts of mediawiki send logs formatted in a different way.
=== No logs indexed ===
This alert is based on the incoming logs per second indexed by OpenSearch. During normal operation there is a baseline of ~1k logs/s (July 2020) and anything significantly lower than that is an unexpected condition. Check the Logstash dashboard attached to alert for signs of root causes. Most likely Logstash has stopped sending logs to OpenSearch.
=== Drop spammy logs ===
Occasionally producers will outpace Logstash's ingestion capabilities, most often with what's considered "log spam" (e.g. dumping whole request/response in debug logs). In these case one solution is to drop the offending logs from Logstash, and ideally the producer has already stopped spamming. The simplest such filter is installed before most/all other filters, matches a few fields and then drops the message:
filter {
 if [program] == "producer" and [nested][field] == "offending value" {
 drop {}
 }
}
See also this Gerrit change for a real-world example.
=== UDP packet loss ===
Logstash 5 locks up from time to time, causing UDP packet loss on the host it is running on. The fix in this case is to restart logstash.service on the host in question.
=== Replace failed disk and rebuild RAID ===
The storage drives on Logstash data are configured in an mdraid RAID0. OpenSearch handles data redundancy, so the rest of the cluster will absorb the impact of the downed node.
Once the disk is replaced, the RAID will have to be rebuilt:
First stop opensearch and disable puppet.
Copy disk partition layout from good disk to new disk
 sfdisk -d /dev/sdb | sfdisk /dev/sdi
determine md device mounted at /srv (/dev/md2 for example) and check mdstat
 cat /proc/mdstat
get array information. make a note of the remaining array members, we'll need this information when rebuilding
 mdadm --query --detail /dev/md2
stop and remove the raid0 array
 mdadm --stop /dev/md2 && mdadm --remove /dev/md2
remove traces of the previous array on the old partitions
 mdadm --zero-superblock /dev/sdb4
 mdadm --zero-superblock /dev/sdc4
 # ... etc
 mdadm --zero-superblock /dev/sdh4
create new raid0 array (WARNING: DISKS MAY BE DIFFERENT)
 mdadm --create --verbose /dev/md/2 --level=0 --raid-devices=8 /dev/sdb4 /dev/sdc4 /dev/sdd4 /dev/sde4 /dev/sdf4 /dev/sdg4 /dev/sdh4 /dev/sdi4
make filesystem
 mkfs.ext4 /dev/md2
workaround systemd mount management by commenting out the old array mount in fstab and issuing a daemon reload
 vim /etc/fstab
 systemctl daemon-reload
add mount point back in with new uuid and mount
 vim /etc/fstab
 mount /srv
check to make sure the disk is mounted and add new array definition to /etc/mdadm/mdadm.conf - also remove old definition
 mdadm --detail --scan
 vim /etc/mdadm/mdadm.conf
update initramfs
 update-initramfs -u
check other arrays for failed partitions and add partitions to them
 mdadm --manage /dev/md0 --add /dev/sdi2
 mdadm --manage /dev/md1 --add /dev/sdi3
make opensearch data directory
 mkdir /srv/opensearch && chown opensearch:opensearch /srv/opensearch
re-enable puppet and run puppet. OpenSearch should start up, join the cluster, and immediately start rebalancing shards.
=== Restore Dashboards from backup ===
From a single collector node, delete all .kibana indexes and restart opensearch-dashboards. Check that the restart created .kibana_1 and aliased it with .kibana. Fetch and unzip the backup and run:
 BACKUP_FILE=<myfile>.ndjson; curl -s -X POST http://localhost:5601/api/saved_objects/_import?createNewCopies=false -H "osd-xsrf: true" --form file=@$BACKUP_FILE > response.json
Check the response for problems and navigate into OpenSearch Dashboards to ensure expected saved objects are present.
== Stats ==
=== Documents and bytes counts ===
The OpenSearch cat API provides a simple way to extract general statistics about log storage, e.g. total logs and bytes (not including replication)
 logstash1010:~$ curl -s 'localhost:9200/_cat/indices?v&bytes=b' | awk '/logstash-/ {b+=$10; d+=$7} END {print d; print b}'
Or logs per day (change $3 to $7 to get bytes sans replication)
 logstash1010:~$ curl -s 'localhost:9200/_cat/indices?v&bytes=b' | awk '/logstash-/ { gsub(/logstash-[^0-9]*/, "", $3); sum[$3] += $7 } END { for (i in sum) print i, sum[i] }' | sort
Or logs per month:
 logstash1010:~$ curl -s 'localhost:9200/_cat/indices?v&bytes=b' | awk '/logstash-/ { gsub(/logstash-[^0-9]*/, "", $3); gsub(/\.[0-9][0-9]$/, "", $3); sum[$3] += $7 } END { for (i in sum) print i, sum[i] }' | sort
== Data Retention ==
Logs are retained in Logstash for a maximum of 90 days by default in accordance with our Privacy Policy and Data Retention Guidelines.
=== Extended Retention ===
See Logstash/Extended Retention
==See also==
*mw:Manual:Structured logging (MediaWiki part of the job to feed into Logstash)
*Logs#mw-log (the old method of viewing logs)
*Introducing Phatality (a Kibana plugin to streamline the process of reporting production errors on Phabricator)
*Kubernetes/Logging How logs flow into Logstash from the Kubernetes components
Category:SRE Observability
Category:Services