Docker Healthcheck

[jguffey]

Hey there, I've got a pretty simple Docker file set up with Node 14 Alpine and a standard next.js install. The important bits are reproduced below.

Dockerfile

FROM node:14.2.0-alpine
ENV SCPATH site
ENV AP /usr/app
EXPOSE 3000
WORKDIR ${AP}
COPY ${SCPATH}/ .
RUN npm install && npm run build
USER node
HEALTHCHECK CMD ["wget", "-q", "localhost:3000"]
CMD ["npm", "start"]

This runs pretty well from the parent docker compose

version: '3'
services:
  spa:
    build:
      context: ../spa
    ports:
      - 8081:3000

However when running from the Docker compose file, the healthchecks never log to output

Successfully built 84b4b42641f2
Successfully tagged docker_spa:latest
Recreating docker_spa_1     ... done
Attaching to docker_spa_1
spa_1        | 
spa_1        | > [email protected] start /usr/app
spa_1        | > next start
spa_1        | 
spa_1        | ready - started server on http://localhost:3000

I believe this is happening because the CMD (npm run start) never returns control to the script. In other words it's not acting like a daemon, instead it's a foreground task. Is there a mode to start the production server in the background? Is that really why Healthchecks are never logging?

Any help is appreciated, thanks!

[jguffey]

Figured out a few things, wget failed because user node either didn't have permission to use wget, or because wget was failing on writing the output. I've tried to fix this by 1) not switching users, so I'm still root in the container, and 2, using curl instead.

I'm also now using pm2 to run next in the background, but still no healthcheck.