Docker

Ember is available as a container image built from scratch (no OS, no shell: just the static binary and CA certificates).

The image is published to both registries with identical content:

• Docker Hub: alexandredaubois/ember
• GitHub Container Registry: ghcr.io/alexandre-daubois/ember

The examples below use the Docker Hub reference; substitute the GHCR one if you prefer.

Quick Start

docker run --rm --network host alexandredaubois/ember

Default Behavior

The image defaults to --daemon --expose :9191. This means:

• No TUI (headless mode)
• Prometheus metrics available on port 9191 (/metrics and /healthz)
• Connects to the Caddy admin API at http://localhost:2019

Network Configuration

Ember needs to reach the Caddy admin API. Two options:

Host Network

Use --network host so the container shares the host's network stack:

docker run --rm --network host alexandredaubois/ember

Custom Address

Point Ember to the Caddy service by name or IP:

docker run --rm alexandredaubois/ember --daemon --expose :9191 --addr http://caddy:2019

Custom Flags

Override the default CMD by appending flags:

docker run --rm --network host alexandredaubois/ember \
  --daemon --expose :9191 --interval 2s --metrics-prefix myapp

Docker Compose

A minimal setup with Caddy and Ember as a sidecar:

services:
  caddy:
    image: caddy:latest
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - ./Caddyfile:/etc/caddy/Caddyfile

  ember:
    image: alexandredaubois/ember
    network_mode: "service:caddy"
    depends_on:
      - caddy

With this setup, Ember runs in the same network namespace as Caddy and can reach localhost:2019 directly.

Caution: The image is built from scratch: there is no shell, no exec, and no debugging tools inside the container. Use docker logs to read Ember's stderr output.

Unix Socket

If Caddy's admin API is configured to listen on a Unix socket, mount the socket into the Ember container:

docker run --rm \
  -v /run/caddy/admin.sock:/run/caddy/admin.sock \
  alexandredaubois/ember \
  --daemon --expose :9191 --addr unix//run/caddy/admin.sock

Or with Docker Compose:

services:
  caddy:
    image: caddy:latest
    volumes:
      - ./Caddyfile:/etc/caddy/Caddyfile
      - caddy-admin:/run/caddy

  ember:
    image: alexandredaubois/ember
    environment:
      EMBER_ADDR: unix//run/caddy/admin.sock
    volumes:
      - caddy-admin:/run/caddy
    depends_on:
      - caddy

volumes:
  caddy-admin:

Multi-instance sidecar

A single Ember container can scrape several Caddy instances and aggregate them behind one Prometheus endpoint:

services:
  caddy-blue:
    image: caddy:latest
    volumes:
      - ./Caddyfile:/etc/caddy/Caddyfile

  caddy-green:
    image: caddy:latest
    volumes:
      - ./Caddyfile:/etc/caddy/Caddyfile

  ember:
    image: alexandredaubois/ember
    environment:
      EMBER_ADDR: blue=http://caddy-blue:2019;green=http://caddy-green:2019
    ports:
      - "9191:9191"
    depends_on:
      - caddy-blue
      - caddy-green

Every emitted Prometheus metric (except ember_build_info) carries an ember_instance="blue" or ember_instance="green" label. See Prometheus Export for details and a recommended metric_relabel_configs snippet.

See Also

• Getting Started
• Prometheus Export