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Real World Elixir Deployment
- 1. REAL WORLD ELIXIR DEPLOYMENT Empire City Elixir | 2016-05-21 pete gamache | [email protected] | @gamache
- 2. Hi!
- 3. Summary • Elixir and Erlang make a rock-solid platform • Erlang excels at long-lived clusters • "Modern" deployment practices do not take advantage of Erlang core features • Deploying Elixir can be painful, but if you are taking advantage of platform, can be worth it
- 4. Let's talk about an ideal platform
- 5. Platform Desirables • Horizontal scalability • Fault tolerance • Zero-downtime upgrades and rollbacks • Stability and performance • Ease of administration and maintenance
- 6. Let's talk about an average platform
- 7. Devops 2010 • Fleets of ephemeral, stateless servers • Load-balancer or shared work queue • All message passing happens externally • All state held externally
- 8. Devops 2010, cont. • Upgrade: Start new servers, add to pool, remove old servers from pool, kill old servers • Rollback: either same as above, or hot/cold a.k.a. blue/green deployment • Many moving parts -- provisioning, load balancer, connection draining
- 9. Devops 2016 • Mostly like that • Something something Docker • Heavily automated • Far-out stuff: virtualized resource pools, e.g. Mesos
- 10. Desirables Achieved? • Horizontal scalability and fault tolerance, check • Zero-downtime upgrades and rollbacks, mostly • Stability and performance, yeah sure • Ease of maintenance, not so sure
- 11. Let's talk about the Erlang platform
- 12. Things Erlang Does • Extreme fault tolerance • Simple scalability to dozens of server nodes • Zero-downtime upgrades/rollbacks (and fast) • Stability and performance
- 13. Things Elixir Helps With • Ease of administration and maintenance
- 14. Erlang Clustering • Designed for long-lived server clusters • Treat OTP apps like microservices, and you get a free resource pool • Postpone sharding • Postpone outboard message passing
- 15. Erlang vs The World • Erlang doesn't look like Devops 2010, but delivers much of Devops 2016 • Go with the flow of the platform • Startups love time-to-market advantages
- 16. Real Talk • Don't use Elixir in prod just because it's shiny • Evaluate advantages and disadvantages • If Elixir and Erlang have the features to get you to market faster or better, consider it • Also consider Erlang + Devops 2016 if that works for your use case • Nothing's free in the long run -- scale hurts
- 17. Deployment • The sum of tools and topology • Topology is a big topic, so here I will abbreviate to "at least two of everything" • Now let's discuss deployment tools on the Erlang/Elixir platform
- 18. In the Beginning... Source: http://learnyousomeerlang.com/relups
- 19. exrm • Elixir Release Manager • Handles most of steps 1-25 in previous slide • Generates Erlang releases • Then you like, put them on servers or something? lol
- 20. edeliver • Based on deliver, a bash-based deploy tool • Works with rebar, mix, relx, exrm • Handles builds, deployment, versioning • Actively developed • https://github.com/boldpoker/edeliver
- 21. How to edeliver • Add edeliver as a dependency/app in mix.exs • Create and configure .deliver/config file • Set up servers, logins, dirs, and configs • Use git tags to mark mix.exs versions • Run mix tasks, make money
- 25. edeliver Directories • Don't create $BUILD_AT, $TEST_AT, $DELIVER_TO yourself • config/*.secret.exs, etc. go in $CONFIG_AT • *.vm.args files handle node names, clustering • Normal Unix permissions rules apply
- 26. How to Clustering • name and setcookie params in vm.args • sync_nodes_mandatory/sync_nodes_optional in :kernel config • http://erlang.org/doc/design_principles/ distributed_applications.html
- 29. edeliver and Versions • edeliver has some new features around auto- versioning • I do not recommend using them (yet) • Just stick to git tags named exactly like the mix.env version (i.e., "0.0.1" not "v0.0.1")
- 30. Let's take edeliver out for a spin
- 31. Build a release
- 36. Build a hot upgrade
- 40. Deploy a hot upgrade
- 45. But they don't always work • Sometimes it's a matter of hand-editing appups and relups • Sometimes packages are not in a position to be hot-upgraded (e.g., Cowboy) • Sometimes f^@% you
- 46. So, What Now? • Rolling upgrades are your best fallback • Necessitates more than one server • Write your code so that function signatures don't change • Above technique is good for DB migrations too!
- 47. Rolling Upgrade • Build release • Deploy release without --start-deploy • Execute on each server: cd $DELIVER_TO/your_app_name releases/X.Y.Z/your_app_name.sh restart
- 48. Rollbacks • Rollbacks are just upgrades • If you could upgrade version X to Y, you can rollback Y to X just as quickly
- 50. Database Migrations • edeliver now has a migration feature • http://blog.plataformatec.com.br/2016/04/ running-migration-in-an-exrm-release/ • I usually just log into the build server and: cd $BUILD_AT/prod MIX_ENV=prod mix ecto.migrate
- 51. Gotcha!
- 52. Gotcha! Ulimit • a.k.a. EFILE, Too many open files • Erlang rules at using file descriptors • It rules so hard that Unix thinks something went wrong and must be contained • Be sure and set ulimit very high/infinite • Set -env ERL_MAX_PORTS very high in vm.args
- 53. Gotcha! Exceptions • Too many exceptions too fast, and the Erlang VM will ragequit • Band-aid Solution 1: -heart in vm.args • Band-aid Solution 2: bin/myapp start in cron • Real Solution: fix your shit
- 54. Gotcha! Segfaults • The Erlang VM is not supposed to segfault • How adorable • Same instructions as previous slide
- 55. Gotcha! Cached Release • Example: you build an upgrade from X to Z • You then build an upgrade from Y to Z • If you had copied X-to-Z to your servers, you can't perform the upgrade Y-to-Z • Solution: Blow away $DELIVER_TO/myapp/ releases/Z before building/deploying Y-to-Z
- 56. Gotcha! Websockets • Unexplained client 400s can be due to load balancer issues • Amazon ELB: use "TCP"/"SSL" settings, not "HTTP"/"HTTPS" • Nginx: proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection "upgrade";
- 58. Finding a Git Solution in edeliver/libexec/erlang
- 61. Another Summary • Erlang and Elixir deployment shouldn't look like less-powerful platforms' • edeliver automates most of the deployment process, mostly. Let's say 90% of the time • Taken next to the platform's advantages, the gotchas aren't so bad • 2016 is early in the Elixir Deployment timeline
- 62. Questions?