Release management

with ExRM and Conform

 

Paul Schoenfelder, ElixirConf 2015

Goals

  • Understand releases (how they are structured, etc.)
  • Be able to leave here knowing how to create and deploy releases
  • Understand release configuration and how Conform can help provide richer, more flexible configuration

OVERview

  • OTP Review
  • How do we deploy Elixir apps?
  • What are releases?
  • How do I use releases?
  • Configuration Management
  • Configuration with Conform

OTP Applications

  • Well defined structure and lifecycle
  • Explicit dependencies
  • Useful metadata (name, version, exports, included apps..)

OTP Application visualized

Release management

  • Install Elixir/Erlang + dependencies (OpenSSL, etc)
  • Push app to target system (tar+scp, git clone, etc.)
  • Configure if necessary
  • Build with MIX_ENV=<target env>
  • Start application with mix run
  • Can be automated (Docker, Heroku buildpack..)

um, without releases.

less than ideal

  • Requires dev dependencies in production
  • Difficult to manage multiple apps with varying Elixir/Erlang version dependencies.
  • No out of the box way to handle application crashes, automatic restarts
  • No option for hot upgrades/downgrades
  • Doesn't work well on some platforms, RaspPi (slow builds), embedded systems (read-only file system)

define better

  • Self-contained applications, with all dependencies
  • No need for production to have tooling installed
  • Application lifecycle management out of the box
  • Path for hot upgrades/downgrades
  • Easy cross-compilation
  • Easy deployment
  • Easily reproduced

Better = OTP Releases

  • Self-contained
  • Lifecycle management (start/stop/restart/up/down)
  • Application health monitoring (heart)
  • Hot upgrades/downgrades
  • Easy cross-compilation
  • Easy deployment
  • Easily reproduced

SO what is a release?

  • Set of versioned OTP applications
  • ERTS (Erlang Runtime System)
  • Release metadata (app startup order, etc.)
  • Explicit configuration (sys.config, vm.args)
  • Scripts for managing the release
  • Packaged as a tarball

RELEASE STRUCTURE

my_app
├── bin
│   ├── my_app/my_app.bat
│   ├── ...
├── erts-7.0.3/
├── lib
│   ├── my_app-0.0.1/
│   ├── ...
├── releases
│   ├── 0.0.1/
│   ├── RELEASES
│   └── start_erl.data

what is exrm?

  • A tool for building releases
  • Extends Relx, the equivalent tool for Erlang
  • Easy to integrate into your existing build process
  • Provides: Mix tasks
  • Provides: Automatic appup generation
  • Provides: Plugin system
  • Provides: Intelligent defaults, but you can still provide your own custom relx.config, vm.args, etc.

MIX RELEASE

  • Read configuration
  • Generates relx.config, sys.config, vm.args
  • Runs before_release hooks
  • Relx: Perform discovery (apps, previous releases)
  • Relx: Resolve dependencies
  • Relx: Build release
  • Relx: Output release to <project>/rel
  • Runs after_release hooks
  • Repackages release
  • Runs after_package hooks

lets take a look

Configuration

  • config.exs + config.<env>.exs
  • Sufficient, but less than ideal for non-programmers
  • Converted to static config (sys.config) in a release
  • Because of this, dynamic configuration, i.e. System.get_env, do not work as expected

ENTER CONFORM

  • Developers define configuration schema
  • Users configure application via init-style config
  • Schema provides config mappings, transforms, validators
  • Extend schemas provided by dependencies
  • Expose important config settings, hide advanced settings, provide documentation, sane defaults
  • Configuration is merged over config.exs settings, so they can co-exist

CONFORM Schema - mappings

  • Define how to map user-facing configuration to system configuration
  • Defines datatype of the setting
  • Defines default values
  • Defines validation rules for the setting
  • Exposes other options (hidden, commented, etc.)
  • Provides documentation

CONFORM Schema - Transforms

  • Functions which receive a reference to the configuration state, and return a value to be used for the given setting
  • Can execute any Elixir/Erlang code (including your own modules)
  • Can be defined in the schema itself, or in a module, by extending a behaviour (Conform.Schema.Transform)

CONFORM Schema - VALIDATORS

  • Functions which receive a mapped value + args, and validate some rule
  • Return :ok, {:warn, msg}, or {:error, msg}
  • Like transforms, can be defined in their own module, by extending a behaviour (Conform.Schema.Validator)
  • Conform provides RangeValidator

HOW CONFORM WORKS

  • Parses .conf
  • Performs mapping + validation
  • Executes transforms
  • Merges parsed config over config.exs/sys.config
  • Outputs sys.config containing final configuration

LETS TAKE A LOOK

Questions?

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