Simple Kemal App

Status: draft example awaiting maintainer verification.

Small Crystal/Kemal app with no database or accessory service. meridian init does not currently auto-detect Kemal projects, so this recipe starts from a hand-written .meridian/deploy.yml.

.meridian/deploy.yml

service: my-app
image: ghcr.io/example/my-app:latest

servers:
  web:
    hosts:
      - prod-01.example.com
    proxy:
      host: app.example.com
      ssl: true
      app_port: 3000
      healthcheck:
        path: /health

env:
  clear:
    KEMAL_ENV: production

ssh:
  user: deploy
  keys:
    - ~/.ssh/id_ed25519

transfer:
  mode: stream

See servers.<role>, servers.<role>.proxy.healthcheck, and transfer.

Containerfile

FROM crystallang/crystal:1.20.2-alpine AS build

WORKDIR /app
RUN apk add --no-cache shards openssl-dev yaml-dev zlib-dev

COPY shard.yml shard.lock ./
RUN shards install --production

COPY . .
RUN crystal build src/server.cr --release -o /out/my-app

FROM alpine:3.21

WORKDIR /app
RUN apk add --no-cache ca-certificates openssl yaml libgcc

COPY --from=build /out/my-app /app/my-app

ENV KEMAL_ENV=production
EXPOSE 3000

CMD ["/app/my-app"]

Kemal Snippet

Use one cheap app health endpoint for Meridian's proxy switch. You can expose additional routes such as /ready for humans or monitoring, but deploy.yml selects one servers.web.proxy.healthcheck.path.

require "kemal"

get "/health" do
  "ok"
end

Kemal.config.port = 3000
Kemal.run

The Kemal app only needs to expose /health. During deploy, Meridian runs the temporary probe container on meridian-proxy.network and calls that endpoint.

Commands

podman build -t ghcr.io/example/my-app:latest .
meridian setup
meridian plan
meridian check
meridian deploy