Docker Template

The Docker template lets you deploy any containerized application. Use it when you want full control over your runtime - Go, Rust, Elixir, or any language with Docker support.

When to use

✅ Good for

Go microservices
Rust web APIs
Elixir/Phoenix apps
Custom runtimes
Existing Dockerized apps

⚠️ Consider alternatives

Python APIs → use backend-service
Next.js sites → use static-site
Fullstack apps → use web-app

Quick start

runtm init docker
cd my-docker-app
# Edit Dockerfile with your application
runtm deploy

Project structure

my-docker-app/
├── runtm.yaml               # Deployment manifest
├── runtm.discovery.yaml     # App metadata (fill in before deploy!)
├── Dockerfile               # Your container build
├── .runtmignore             # Artifact exclusions
└── [your application code]

Requirements

Your Dockerfile must:

Expose the correct port

Match the port in runtm.yaml (default: 8080)

Implement health endpoint

GET /health must return HTTP 200

Start quickly

Application must be ready within 10 seconds

Manifest

The docker template uses a minimal manifest:

runtm.yaml

name: my-docker-app
template: docker
port: 8080
health_path: /health
tier: starter

The docker template doesn’t require a runtime field since you provide your own Dockerfile.

Example Dockerfiles

Go
Rust
Elixir

FROM golang:1.21-alpine AS builder
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -o main .

FROM alpine:latest
WORKDIR /app
COPY --from=builder /app/main .
EXPOSE 8080
CMD ["./main"]

Health endpoint:

http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
    w.WriteHeader(http.StatusOK)
    w.Write([]byte("OK"))
})

FROM rust:1.75-slim AS builder
WORKDIR /app
COPY Cargo.toml Cargo.lock ./
COPY src ./src
RUN cargo build --release

FROM debian:bookworm-slim
COPY --from=builder /app/target/release/myapp /usr/local/bin/
EXPOSE 8080
CMD ["myapp"]

Health endpoint (Axum):

async fn health() -> &'static str {
    "OK"
}

let app = Router::new()
    .route("/health", get(health));

FROM elixir:1.15-alpine AS builder
ENV MIX_ENV=prod
WORKDIR /app
COPY mix.exs mix.lock ./
RUN mix deps.get --only prod
COPY . .
RUN mix release

FROM alpine:latest
COPY --from=builder /app/_build/prod/rel/myapp ./
EXPOSE 8080
CMD ["bin/myapp", "start"]

Health endpoint (Phoenix):

# router.ex
get "/health", HealthController, :check

# health_controller.ex
def check(conn, _params) do
  send_resp(conn, 200, "OK")
end

Environment variables

Declare environment variables in your manifest:

runtm.yaml

env_schema:
  - name: DATABASE_URL
    type: string
    required: true
    secret: true
    description: "Database connection string"
  - name: LOG_LEVEL
    type: string
    required: false
    default: "info"

Set secrets locally:

runtm secrets set DATABASE_URL=postgres://...
runtm secrets list

Machine tiers

Tier	Memory	CPUs	Best for
`starter`	256 MB	1 shared	Simple APIs, low traffic
`standard`	512 MB	1 shared	Most workloads
`performance`	1 GB	2 shared	Heavy processing

Set in your manifest:

runtm.yaml

tier: standard

Deployment checklist

Replace Dockerfile

Replace the placeholder with your application build

Implement health endpoint

Ensure GET /health returns HTTP 200

Test locally

docker build -t my-app .
docker run -p 8080:8080 my-app
curl http://localhost:8080/health

Update discovery metadata

Edit runtm.discovery.yaml and replace all # TODO: placeholders

Deploy

runtm validate
runtm deploy

Constraints

Constraint	Requirement
Port	Must match `runtm.yaml` (default: 8080)
Health endpoint	Must return 200 at `/health`
Startup time	Must be ready within 10 seconds
Artifact size	Must be under 20MB (use `.runtmignore`)

The placeholder Dockerfile in the template is for demonstration only. You must replace it with your actual application build.

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Docker Template

When to use

✅ Good for

⚠️ Consider alternatives

Quick start

Project structure

Requirements

Manifest

Example Dockerfiles

Environment variables

Machine tiers

Deployment checklist

Constraints

​When to use

✅ Good for

⚠️ Consider alternatives

​Quick start

​Project structure

​Requirements

​Manifest

​Example Dockerfiles

​Environment variables

​Machine tiers

​Deployment checklist

​Constraints

When to use

Quick start

Project structure

Requirements

Manifest

Example Dockerfiles

Environment variables

Machine tiers

Deployment checklist

Constraints