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?