MediaWiki On Kubernetes
MediaWiki-on-Kubernetes (or mw-on-k8s for short) is an initiative to transition the MediaWiki at WMF deployment from dedicated Application servers to Kubernetes. This page contains information about what is changing as part of this transition.
Motivation
"This migration will unleash the ability to deploy multiple versions of code simultaneously. Also, this will help enhance platform capabilities to build dockerized isolated environments for coding, testing and even production debugging.
MediaWiki on Kubernetes will allow us to deprecate and eventually remove a lot of our in-house developed code. Another benefit is that we will be able to react to sudden traffic spikes, like newsworthy events better, as the flexing up and down is a matter of configuration change. This enables efficient placement of workloads, packing workloads in a more environmentally friendly way, increasing hardware utilization."[1]
What traffic is currently served by MediaWiki on k8s
External traffic
As of today, 100% of all external traffic is served by MediaWiki on k8s (config file).
Exceptions
Internal traffic
As of today, MediaWiki on k8s serves all internal API traffic.
Exceptions
- Possibly yet-unidentified stragglers (Unknown Unknowns)
Jobs
As of today, jobs are handled by MediaWiki on k8s
Exceptions
- videoscaling
Progress can be followed through this Phabricator task
Server groups
MediaWiki on Kubernetes is deployed to both the main Eqiad and Codfw datacenters, in the wikikube
kubernetes clusters. While the situation is in constant evolution, we currently have the following server groups:
Deployment | Port | Description |
---|---|---|
mw-debug |
4444 | For external requests with X-Wikimedia-Debug, like the old mwdebug VMs. Accessible using the k8s-mwdebug option of the WikimediaDebug browser extension.
|
mw-web |
4450 | For external requests from web browsers (via the CDN). |
mw-api-ext |
4447 | For external requests to the API (via the CDN). |
mw-api-int |
4446 | For internal requests to the API (from other services). |
mw-jobrunner |
4448 | For internal requests from the JobQueue runners (except videoscaling jobs). |
mw-parsoid |
4452 | For requests that used to be processed by the parsoid-php cluster |
mw-misc |
30443 (ingress) | Miscellaneous mediawiki installs |
mw-wikifunctions |
4451 | wikifunctions dedicated deployment |
What is in a MediaWiki pod
Each MediaWiki pod in Kubernetes contains 8 containers:
mediawiki-main-tls-proxy
- running Envoy, as service mesh and TLS terminator.mediawiki-main-httpd
- running the Apache httpd daemon.mediawiki-main-app
- running the PHP daemon.mediawiki-main-mcrouter
- running mcrouter.mediawiki-main-rsyslog
- running rsyslog, to collect MediaWiki logs (for Logstash) and Apache access logs.mediawiki-main-{php-fpm,mcrouter,httpd}-exporter
- the Prometheus exporters for PHP, mcrouter and Apache httpd.
For more detailed information please see our MediaWiki On Kubernetes/How it works page.
How to manage changes to the infrastructure
Given we're in a transition phase between the old puppet-managed systems and MediaWiki running on Kubernetes, we tried to keep things shared as much as possible. This means that deploying Puppet changes for app servers influences future mw-on-k8s deploys. However, Puppet merely prepares the host where the Kubernetes images are built, it doesn't perform a Kubernetes deployment. Applying infra-level changes to Kubernetes services and doing a code deployment are exactly the same procedure, but we need additional care when merging infrastructure changes.
Things that propagate from Puppet to MediaWiki-on-Kubernetes include:
- The list of logging brokers, and the udp2log host.
- The list of service proxy endpoints to offer, and the list of all available too (out of service::catalog).
- The list of MediaWiki sites and Apache configuration parameters (e.g. which domain names for Apache vhosts), but not the Apache config template itself!
- The list of memcached servers.
- The GeoIP and GeoIPInfo data
So, whenever you want to change any of the above things, you will need to:
- check what your change would modify on a
role::deployment_server::kubernetes
host - if it changes a file under/etc/helmfile-defaults/mediawiki
then the following applies to your change - only merge the change during a "MediaWiki infrastructure" window routinely scheduled on Deployments calendar, or otherwise well outside of any MediaWiki code deployment window. This is done to allow both SREs and MW developers/deployers to monitor their deployments independently and avoid unexpected consequences.
- after the change is merged, ensure a puppet run happens on the MediaWiki deployment server, then proceed to re-deploy all MediaWiki service groups on Kubernetes.
How to deploy MediaWiki on Kubernetes
Add a mw-on-k8s deployment
to scap
In order for scap to deploy to your mw-on-k8s deployment, an entry must be added to the profile::kubernetes::deployment_server::mediawiki::release::mw_releases
configuration in puppet's hieradata/role/common/deployment_server/kubernetes.yaml
.
The entry format is changing (see task T370934) and it's recommended to use the new format like the following example, here assuming that you have a single primary release named main
and a canaries-stage release named canary
:
- namespace: mw-mydeployment
releases:
main: {}
canary:
stage: canaries
mw_flavour: "publish"
web_flavour: "webserver"
debug: false
This is equivalent to the older format:
- namespace: mw-mydeployment
release: main
canary: canary
mw_flavour: "publish"
web_flavour: "webserver"
debug: false
Both formats are currently supported by scap as of this writing.
to the cookbooks
Add the new mediawiki deployment to the list(s) of mediawiki services in cookbooks/sre/switchdc/mediawiki/__init__.py
, like https://gerrit.wikimedia.org/r/c/operations/cookbooks/+/969131
Manual deployment
scap sync-world --stop-before-sync
rebuilds the image and updates the Helmfile release files, so you can call helmfile apply afterwards to manually update the releases
Automatic deployment
scap sync-world --k8s-only
rebuilds the image and only triggers the deployment to mw-on-k8s, leaving the regular Apache targets untouched
Note:
- The
--pause-after-testserver-sync
flag will pause deployment aftermw-debug
is updated and wait for confirmation. If you are deploying changes that warrant manual verification againstmw-debug
, consider using this. scap
will not display helmfile diffs before deployment by default. If you are deploying helmfile changes that need careful sequencing, consider either:- verifying these manually using
helmfile diff
- using
scap
's--k8s-confirm-diffs
option
- verifying these manually using
Full image rebuild and deployment
This can be useful especially when we need to update a base image:
scap sync-world --k8s-only --k8s-confirm-diff -D full_image_build:true
No image build deployment (helmfile only)
The scap way
user@deploy:~$ scap sync-world --k8s-only --k8s-confirm-diff -Dbuild_mw_container_image:False
For changes that need extra manual verification (e.g., Apache configuration) or sequencing, see Notes in Automatic deployment above.
The bash way
This should be limited to deploying one or two Mediawiki-On-Kubernetes deployments. Deploying to all should be done with scap.
# Deploy mw-debug
user@deploy:~$ cd /srv/deployment-charts/helmfile.d/services/mw-debug
user@deploy:/srv/deployment-charts/helmfile.d/services/mw-debug$ helmfile -e codfw -i apply --context 5 && helmfile -e eqiad -i apply --context 5
# Deploy a couple Mediawiki-On-Kubernetes deployments
user@deploy:~$ cd /srv/deployment-charts/helmfile.d/services
user@deploy:/srv/deployment-charts/helmfile.d/services$ for i in mw-api-int mw-api-ext mw-wikifunctions; do (cd $i && helmfile -e codfw -i apply --context 5 && helmfile -e eqiad -i apply --context 5 ) ; done
Troubleshooting
Dashboards
Logs
- Apache2 AccessLog dashboard (OpenSearch)
- php-fpm slowlog dashboard (OpenSearch)
- php-fpm errrolog dashboard (OpenSearch)
Graphs
MediaWiki REPL
Any deployer can launch, from a deployment server, a REPL shell (either shell.php
or eval.php
) using the mw-debug-repl
script:
you@deploy1002 $ sudo mw-debug-repl
Error: a wiki should be provided on the command line
mw-debug-repl - launch a MediaWiki REPL in the kubernetes mw-debug environment.
Usage: mw-debug-repl [-e] [-d <datacenter>] [-w <wiki-name>|<wiki-name>]
OPTIONS:
-e Launch eval.php, instead of the default shell.php as REPL
-d|--datacenter Pick a specific datacenter (by default the master will be picked)
-w|--wiki Pick a wiki. For compatibility reasons, the flag can be omitted.
-h|--help Show this help message
EXAMPLES:
Launch an eval.php shell for itwiki in eqiad
$ sudo /usr/local/bin/mw-debug-repl -e -d eqiad --wiki itwiki
# Also valid:
$ sudo /usr/local/bin/mw-debug-repl -e --datacenter eqiad itwiki
Launch shell.php for enwiki
$ sudo /usr/local/bin/mw-debug-repl enwiki
$ sudo /usr/local/bin/mw-debug-repl --wiki enwiki
you@deploy1002 $ sudo mw-debug-repl enwiki
Finding a mw-debug pod in eqiad...
Now running shell.php for enwiki inside pod/mw-debug.eqiad.pinkunicorn-59b5df7ffd-h2xxq...
Psy Shell v0.11.10 (PHP 7.4.33 — cli) by Justin Hileman
> echo $wmgServerGroup
kube-mw-debug⏎
>
Get a shell on a production pod
you@deploy1002 $ sudo -i
root@deploy1002 # kube-env admin eqiad
root@deploy1002 # kubectl -n mw-web get pods
NAME READY STATUS RESTARTS AGE
mw-web.eqiad.canary-68998c7b48-2jt8g 8/8 Running 0 2d13h
mw-web.eqiad.canary-68998c7b48-r5hng 8/8 Running 0 2d13h
mw-web.eqiad.main-7f65fbb9c8-69sm2 8/8 Running 0 2d13h
mw-web.eqiad.main-7f65fbb9c8-7vtrl 8/8 Running 0 2d13h
mw-web.eqiad.main-7f65fbb9c8-9rr9l 8/8 Running 0 2d13h
mw-web.eqiad.main-7f65fbb9c8-gjgrk 8/8 Running 0 2d13h
mw-web.eqiad.main-7f65fbb9c8-j88nr 8/8 Running 0 2d13h
mw-web.eqiad.main-7f65fbb9c8-lpq9f 8/8 Running 0 2d13h
mw-web.eqiad.main-7f65fbb9c8-lwhwj 8/8 Running 0 2d13h
mw-web.eqiad.main-7f65fbb9c8-xr64t 8/8 Running 0 2d13h
root@deploy1002 # kubectl -n mw-web exec pod/mw-web.eqiad.main-7f65fbb9c8-69sm2 -c mediawiki-main-app -it -- /bin/bash
www-data@mw-web:/$
strace a production PHP process
root@deploy1002 # kubectl -n mw-web describe pod mw-web.eqiad.main-7f65fbb9c8-69sm2 | grep Node:
Node: kubernetes1023.eqiad.wmnet/10.64.32.21
root@deploy1002 # kubectl -n mw-web exec pod/mw-web.eqiad.main-7f65fbb9c8-69sm2 -c mediawiki-main-app -- ps -eo pid,pidns,args
PID PIDNS COMMAND
1 4026533595 php-fpm: master process (/etc/php/7.4/fpm/php-fpm.conf)
1345418 4026533595 php-fpm: pool www
1346141 4026533595 php-fpm: pool www
1346193 4026533595 php-fpm: pool www
1346539 4026533595 php-fpm: pool www
1346750 4026533595 php-fpm: pool www
1346818 4026533595 php-fpm: pool www
1348934 4026533595 php-fpm: pool www
1349988 4026533595 php-fpm: pool www
2367349 4026533595 ps -eo pid,pidns,args
Let's strace PID 1346750 in the container. The container doesn't have strace, but we can run it on the host. But it's in a PID namespace so we have to figure out what the PID is in the root namespace. In the host, /proc/$pid/status contains the PID in both the container's namespace and the root namespace. We can confirm the identification by checking that the pidns is the same.
$ ssh kubernetes1023.eqiad.wmnet
you@kubernetes1023 $ grep NStgid.*1346750 /proc/*/status
/proc/69585/status:NStgid: 69585 1346750
you@kubernetes1023 $ sudo ps -p 69585 -o pidns
PIDNS
4026533595
you@kubernetes1023 $ sudo strace -p 69585
strace: Process 69585 attached