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Switch Datacenter

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Revision as of 17:54, 19 April 2016 by imported>Alex Monk (new sub-step for future MW switches: be careful about RC)
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Introduction

A datacenter switchover (from eqiad to codfw, or vice-versa) comprises switching over multiple different components, some of which can happen independently and many of which need to happen in lockstep. This page documents all the steps needed to switch over from a master datacenter to another one, broken up by component.

Schedule for Q3 FY2015-2016 rollout

  • Deployment server: Wednesday, January 20th
  • Traffic: Thursday, March 10th
  • MediaWiki 5-minute read-only test: Tuesday, March 15th 07:00 UTC
  • ElasticSearch: Thursday, April 7th, 12:00 UTC
  • Media storage/Swift: Thursday, April 14th 17:00 UTC
  • Services: Monday, April 18th, 10:00 UTC
  • MediaWiki: Tuesday, April 19th, 14:00 UTC / 07:00 PDT / 16:00 CEST (requires read-only mode)

Switching back

  • MediaWiki: Thursday, April 21st, 14:00 UTC / 07:00 PDT / 16:00 CEST (requires read-only mode)
  • Services, ElasticSearch, Traffic, Swift, Deployment server: Thursday, April 21st, after the above is done


Per-service switchover instructions

MediaWiki-related

  1. Warm up databases; also see manual cache warmup.
  2. Stop jobqueues in eqiad
  3. Stop all jobs running on the maintenance host
  4. Deploy mediawiki-config with all shards set to read-only
  5. Set eqiad databases (masters) in read-only mode.
  6. Wipe codfw memcached to prevent stale values. Once eqiad is read-only and cofdw read-only master/slaves are caught up; any subsequent requests to codfw that set memcached are fine. Run salt -C 'G@cluster:memcached and G@site:codfw' cmd.run 'service memcached restart'
  7. Switch the datacenter in puppet
    • Set $app_routes['mediawiki'] = 'codfw' in puppet (cherry-pick https://gerrit.wikimedia.org/r/282898)
    • $wmfMasterDatacenter in mediawiki-config (https://gerrit.wikimedia.org/r/#/c/282897/). This has several consequences:
    • Redis replication will be flowing codfw => eqiad once puppet has ran
      first in codfw salt 'mc2*' cmd.run 'puppet agent -t'; salt 'rdb2*' cmd.run 'puppet agent -t'
      and then in eqiad salt 'mc1*' cmd.run 'puppet agent -t'; salt 'rdb1*' cmd.run 'puppet agent -t'
    • RESTBase (needs puppet run + service restart): salt -b10% -G 'cluster:restbase' cmd.run 'puppet agent -t; service restbase restart'
    • All other services will be automatically reconfigured whenever puppet runs after $app_routes is modified salt 'sc*' cmd.run 'puppet agent -t'
  8. Parsoid switch of the action API endpoint (manages its own config, will need a deploy + restart of its own)
  9. Deploy Varnish to switch backend to appserver.svc.codfw.wmnet/api.svc.codfw.wmnet
  10. Point Swift imagescalers to the active MediaWiki
    • Merge https://gerrit.wikimedia.org/r/#/c/268080/
    • run puppet on ms-fe* plus swift-init all reload for the changes to take effect, eqiad salt -b1 'ms-fe1*' cmd.run 'puppet agent -t; swift-init all reload' and codfw salt -b1 'ms-fe2*' cmd.run 'puppet agent -t; swift-init all reload'
  11. Database master swap for every core (s1-7), External Storage (es2-3, not es1), parsercache (pc) and extra (x1) database
    • Deploy puppet $master = true for the appropriate hosts. https://gerrit.wikimedia.org/r/284144 (Make sure pt-heartbeat-wikimedia is running on the new hosts and not on the old ones by applying the parameter change on all masters)
    • Make sure all masters, including the inactive ones are using STATEMENT-based replication (required for labs filtering)
    • Set codfw masters mysql as read-write
    • Change *-master dns to the new masters (only used by humans)
  12. Deploy mediawiki-config codfw with all shards set to read-write
  13. Start the jobqueue in codfw
  14. Start the cron jobs on the maintenance host in codfw

Debugging

You can force Varnish to pass a request to a backend in codfw or eqiad using the X-Wikimedia-Debug header.

For codfw, use X-Wikimedia-Debug: backend=mw2017.codfw.wmnet

For eqiad, use X-Wikimedia-Debug: backend=mw1017.eqiad.wmnet

Media storage/Swift

Ahead of the switchover, originals and thumbs

  1. MediaWiki: Write synchronously to both eqiad/codfw with https://gerrit.wikimedia.org/r/#/c/282888/
  2. Cache->app: Change varnish backends for swift and swift_thumbs to point to codfw with https://gerrit.wikimedia.org/r/#/c/282890/
    1. Force a puppet run on cache_upload in eqiad + codfw: salt -v -t 10 -b 17 -C 'G@cluster:cache_upload and ( G@site:eqiad or G@site:codfw )' cmd.run 'puppet agent --test'
  3. Inter-Cache: Switch codfw from 'eqiad' to 'direct' in cache::route_table for upload https://gerrit.wikimedia.org/r/#/c/282891/
    1. Force a puppet run on cache_upload in codfw: salt -v -t 10 -b 17 -C 'G@cluster:cache_upload and G@site:codfw' cmd.run 'puppet agent --test'
  4. Users: De-pool eqiad in GeoDNS https://gerrit.wikimedia.org/r/#/c/283416/ + authdns-update
  5. Inter-Cache: Switch esams from 'eqiad' to 'codfw' in cache::route_table for upload https://gerrit.wikimedia.org/r/#/c/283418/
    1. Force a puppet run on cache_upload in esams: salt -v -t 10 -b 17 -C 'G@cluster:cache_upload and G@site:esams' cmd.run 'puppet agent --test'
  6. Inter-Cache: Switch eqiad from 'direct' to 'codfw' in cache::route_table for upload https://gerrit.wikimedia.org/r/#/c/282892/
    1. Force a puppet run on cache_upload in eqiad: salt -v -t 10 -b 17 -C 'G@cluster:cache_upload and G@site:eqiad' cmd.run 'puppet agent --test'

ElasticSearch

Point CirrusSearch to codfw by editing wmgCirrusSearchDefaultCluster InitialiseSettings.php. The usual default value is "local", which means that if mediawiki switches DC, everything should be automatic. For this specific switch, the value has been set to "codfw" to switch Elasticsearch ahead of time.

Traffic

GeoDNS user routing

Inter-Cache routing

Cache->App routing

Specifics for Switchover Test Week

After switching all applayer services we plan to switch successfully, we'll switch user and inter-cache traffic away from eqiad:

  • The Upload cluster will be following similar instructions on the 14th during the Swift switch.
  • Maps and Misc clusters are not participating (low traffic, special issues, validated by the other moves)
  • This leaves just the text cluster to operate on below:
  1. Inter-Cache: Switch codfw from 'eqiad' to 'direct' in cache::route_table for the text cluster.
  2. Users: De-pool eqiad in GeoDNS for the text cluster.
  3. Inter-Cache: Switch esams from 'eqiad' to 'codfw' in cache::route_table for the text cluster.
  4. Inter-Cache: Switch eqiad from 'direct' to 'codfw' in cache::route_table for the text cluster.

Before reversion of applayer services to eqiad, we'll revert the above steps in reverse order to undo them:

  1. Inter-Cache: Switch eqiad from 'codfw' to 'direct' in cache::route_table for all clusters.
  2. Inter-Cache: Switch esams from 'codfw' to 'eqiad' in cache::route_table for all clusters.
  3. Users: Re-pool eqiad in GeoDNS.
  4. Inter-Cache: Switch codfw from 'direct' to 'eqiad' in cache::route_table for all clusters.

Services

  • RESTBase and Parsoid already active in codfw, using eqiad MW API.
  • Shift traffic to codfw:
    • Public traffic: Update Varnish backend config.
    • Update RESTBase and Flow configs in mediawiki-config to use codfw.
  • During MW switch-over:

Other miscellaneous