Phoenix Operations and Deployment (Elixir/BEAM)

Production-ready Phoenix apps rely on releases, runtime configuration, telemetry, clustering, and secure endpoints. The BEAM enables rolling restarts and supervision resilience when configured correctly.

Releases and Runtime Config

bash

MIX_ENV=prod PHX_SERVER=true mix assets.deploy
MIX_ENV=prod mix release
_build/prod/rel/my_app/bin/my_app eval "IO.puts(:os.type())"
_build/prod/rel/my_app/bin/my_app start

config/runtime.exs

for env-driven settings:

elixir

config :my_app, MyApp.Repo,
  url: System.fetch_env!("DATABASE_URL"),
  pool_size: String.to_integer(System.get_env("POOL_SIZE", "10")),
  ssl: true

config :my_app, MyAppWeb.Endpoint,
  url: [host: System.fetch_env!("PHX_HOST"), port: 443, scheme: "https"],
  http: [ip: {0,0,0,0}, port: String.to_integer(System.get_env("PORT", "4000"))],
  secret_key_base: System.fetch_env!("SECRET_KEY_BASE"),
  server: true

Secrets

Prefer env vars or secret stores (AWS/GCP KMS, Vault); avoid embedding in configs.
Generate
```
SECRET_KEY_BASE
```
with
```
mix phx.gen.secret
```
.

Clustering and PubSub/Presence

Add

libcluster

for automatic node discovery:

elixir

# mix.exs deps
{:libcluster, "~> 3.3"},
{:phoenix_pubsub, "~> 2.1"},

# application.ex
topologies = [
  dns_poll: [
    strategy: Cluster.Strategy.DNSPoll,
    config: [poll_interval: 5_000, query: "my-app.internal"],
    connect: {:net_adm, :ping}
  ]
]

children = [
  {Cluster.Supervisor, [topologies, [name: MyApp.ClusterSupervisor]]},
  {Phoenix.PubSub, name: MyApp.PubSub},
  MyAppWeb.Endpoint
]

Guidelines

Share
```
secret_key_base
```
across nodes for consistent session signing.
Use distributed PubSub for Presence; ensure node connectivity before enabling Presence-heavy features.
For blue/green, keep cookies compatible between versions.

Telemetry, Logging, and Metrics

Install
```
opentelemetry_phoenix
```
and
```
opentelemetry_ecto
```
for traces/metrics.
Add
```
Plug.Telemetry
```
and
```
LoggerJSON
```
or structured logging.
Export metrics (Prometheus/OpenTelemetry) via
```
:telemetry_poller
```
for VM stats (reductions, memory, schedulers).
Set
```
LOGGER_LEVEL=info
```
in prod; use
```
:debug
```
only for troubleshooting.

HTTP and Network Hardening

Enforce HTTPS (
```
force_ssl
```
), HSTS, secure cookies (
```
same_site
```
,
```
secure
```
), and proper
```
content_security_policy
```
.
CORS: configure
```
cors_plug
```
for API origins.
Rate limiting: apply plugs (ETS/Cachex token bucket) or edge (NGINX/Cloudflare).
Uploads: prefer presigned URLs; limit request body size (
```
:max_request_line_length
```
,
```
:max_header_value_length
```
).

Assets and Static Delivery

```
mix assets.deploy
```
runs npm/tailwind/esbuild and digests assets.
Serve static files via CDN/reverse proxy; ensure
```
cache-control
```
headers set in Endpoint.
Disable unused watchers in production to trim image size.

Background Jobs

Oban recommended for retries/backoff, scheduled jobs, and isolation; supervise in
```
application.ex
```
.
Configure queues via runtime env; monitor with Oban Web/Pro or telemetry.
For CPU-heavy tasks, consider pooling or external workers to avoid blocking schedulers.

Deployment Patterns

Containers: multi-stage builds; run

mix deps.get --only prod

mix compile

mix assets.deploy

, then

mix release

Systemd: run release binary as service with
```
Environment=
```
secrets; add
```
Restart=on-failure
```
.
Fly/Gigalixir/Render: supply env vars, attach Postgres/Redis, open long-lived WebSocket ports.
Blue/green or canary: keep DB migrations compatible; deploy code first, then run migrations; keep feature flags for schema changes.

Observability and Health

Add
```
/health
```
and
```
/ready
```
endpoints (Repo check + PubSub/Presence check).
Export VM metrics: run
```
:telemetry_poller
```
for scheduler utilization and memory.
Alert on error rates, DB timeouts, queue depths, and VM memory.

Common Pitfalls

Building releases without
```
PHX_SERVER=true
```
(endpoint won’t start).
Missing runtime config in
```
config/runtime.exs
```
; relying on compile-time config for secrets.
No cluster discovery configured → Presence inconsistencies across nodes.
Leaving default
```
secret_key_base
```
or per-node keys → invalid sessions after deploy.
Large assets without digests/CDN → slow cold loads.

phoenix-ops

NPX Install

Tags

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