MySQL High Availability at GitHub

by Shlomi Noach

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MySQL   High Availability   at GitHub Shlomi Noach GitHub 2018

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Agenda MySQL @ GitHub The HA story orchestrator Old vs. new design Testing Thoughts

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About me @github/database-infrastructure Author of orchestrator, gh-ost, freno, ccql and others. Blog at http://openark.org   github.com/shlomi-noach  @ShlomiNoach

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GitHub Built for Developers Largest open source hosting 67M repositories, 24M users Critical path in build flows Best octocat T-Shirts and stickers

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MySQL at GitHub Stores all the metadata: users, repositories,   commits, comments, issues, pull requests, … Serves web, API and auth traffic MySQL 5.7, semi-sync replication, RBR, cross DC ~15 TB of MySQL tables ~150 production servers, ~15 clusters Availability is critical

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MySQL High Availability We wish to have: Automation, reliable detection, DC tolerant failovers, DC isolation tolerance, reasonable failover time, reliable failover, lossless where possible.

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MySQL High Availability Write HA/read HA

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MySQL High Availability Detection Recovery Master discovery

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orchestrator

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orchestrator, meta Adopted, maintained & supported by GitHub,   github.com/github/orchestrator Previously at Outbrain and Booking.com Orchestrator is free and open source, released under the Apache 2.0 license  github.com/github/orchestrator/releases Gaining wider adoption ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

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orchestrator Discovery  Probe, read instances, build topology graph, attributes, queries Refactoring  Relocate replicas, manipulate, detach, reorganize Recovery  Analyze, detect crash scenarios, structure warnings, failovers, promotions, acknowledgements, flap control, downtime, hooks ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

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orchestrator @ GitHub orchestrator/raft deployed on 3 DCs Automated failover for masters and intermediate masters Chatops integration !

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How is orchestrator diﬀerent? Holistic approach to failure detection State based, elaborate recovery decision making !

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Detection: naive approach Probe the master Test failure? Try again n times, interval i ! !

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Detection: holistic approach orchestrator: Probe the master and its replicas Expect agreement Agreement achieved? The cluster is de-facto down. ! ! ! ! !

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Configuration indicates which servers whitelisted or blacklisted. Production operations must reflect in configuration changes. Promote the most up-to-date replica. Promotion: naive assumptions ! ! ! ! 5.6  SBR 5.7  RBR 5.7  RBR, must_not DC1

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orchestrator: Recognizes environments are dynamic Understands replication rules Resolves version, DC, config, promotion rules Acts based on state Promotion constraints: real life ! ! ! ! 5.6  SBR 5.7  RBR 5.7  RBR, must_not DC1

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orchestrator can promote one, non-ideal replica, have the rest of the replicas converge,     and then refactor again, promoting an ideal server. Promotion constraints: real life ! ! ! ! most up-to-date  DC2 less up-to-date  DC1 No binary logs  DC1 DC1

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Earlier master discovery   @ GitHub VIP + DNS based

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" " " ! ! ! ! ! ! ! ! ! ! ! ! ! ! app ⋆ ⋆ ⋆ DNS DNS ! ! ! orchestrator Master discovery via VIP+DNS

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Earlier master discovery   @ GitHub Cooperative, long, not a good cross-DC story

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GLB/HAProxy anycast Consul orchestrator semi-synchronous replication A better story

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orchestrator/Consul/GLB(HAProxy) @ GitHub $ $ $ ! ! ! ! ! ! ! ! ! ! ! ! ! ! glb/proxy % Consul * n " " " % Consul * n ! ! ! app orchestrator/  raft

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A better story More components, but less moving parts. Better ownership Decoupling

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GLB High available, scalable proxy array Lossless reloads, implicit SSL, consul integration GLB director, load balancer array via HAProxy  https://githubengineering.com/introducing-glb/  https://githubengineering.com/glb-part-2-haproxy-zero-downtime-zero-delay-reloads- with-multibinder/ 

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Consul By HashiCorp  https://consul.io/ Mozilla Public License 2.0  https://github.com/hashicorp/consul

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Consul Service Discovery Health checks, DNS, KV storage Highly available

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consul-template Simple template engine Listens to Consul updates

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orchestrator/raft A highly available orchestrator setup Self healing Cross DC Mitigates DC partitioning ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

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orchestrator/raft 2 nodes per DC + mediator more to come Added raft features: • Step down • Yield • SQLite log store !

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orchestrator/Consul/GLB(HAProxy) @ GitHub $ $ $ ! ! ! ! ! ! ! ! ! ! ! ! ! ! glb/proxy % Consul * n " " " % Consul * n ! ! ! app orchestrator/  raft

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orchestrator owns recovery, updates Consul consul-template runs on GLB servers, reconfigures & reloads GLB GLB reroutes connections Hard-kill old connections Apps connect via anycast, route through local GLB Independent Consul deployments per DC are managed by orchestrator/raft orchestrator/Consul/GLB(HAProxy) @ GitHub

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semi-synchronous replication Lossless, best effort 500ms timeout Effectively picks our ideal candidates

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Results Reliable detection Recovery in: 10s - 13s (total outage time) , normal case 15s - 20s, difficult case 25s, rare

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Cons App identity unkown Distributed system, calls for a variety of scenarios STONITH, work in progress

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Testing Testing cluster in production environment Continuously kill/block/reject

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