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83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
# Bootstrap container using node command instead of npm
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## One paragraph explainer
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We are used to see code examples where folks start their app using `CMD 'npm start'`. This is a bad practice. The `npm` binary will not forward signals to your app which prevents graceful shutdown (see [/sections/docker/graceful-shutdown.md]). If you are using child-processes they won’t be cleaned up correctly in case of unexpected shutdown, leaving zombie processes on your host. `npm start` also results in having an extra process for no benefit. To start you app use `CMD ['node','server.js']`. If your app spawns child-processes also use `TINI` as an entrypoint.
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### Code example - Bootsraping using Node
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```dockerfile
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FROM node:12-slim AS build
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WORKDIR /usr/src/app
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COPY package.json package-lock.json ./
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RUN npm ci --production && npm clean cache --force
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CMD ["node", "server.js"]
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```
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### Code example - Using Tiny as entrypoint
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```dockerfile
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FROM node:12-slim AS build
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# Add Tini if using child-processes
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ENV TINI_VERSION v0.19.0
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ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini
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RUN chmod +x /tini
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WORKDIR /usr/src/app
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COPY package.json package-lock.json ./
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RUN npm ci --production && npm clean cache --force
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ENTRYPOINT ["/tini", "--"]
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CMD ["node", "server.js"]
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```
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### Antipatterns
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Using npm start
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```dockerfile
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FROM node:12-slim AS build
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WORKDIR /usr/src/app
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COPY package.json package-lock.json ./
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RUN npm ci --production && npm cache clean --force
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# don’t do that!
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CMD "npm start"
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```
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Using node in a single string will start a bash/ash shell process to execute your command. That is almost the same as using `npm`
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```dockerfile
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FROM node:12-slim AS build
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WORKDIR /usr/src/app
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COPY package.json package-lock.json ./
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RUN npm ci --production && npm clean cache --force
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# don’t do that, it will start bash
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CMD "node server.js"
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```
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Starting with npm, here’s the process tree:
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```console
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$ ps falx
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UID PID PPID COMMAND
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0 1 0 npm
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0 16 1 sh -c node server.js
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0 17 16 \_ node server.js
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```
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There is no advantage to those two extra processes.
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Sources:
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https://maximorlov.com/process-signals-inside-docker-containers/
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https://github.com/nodejs/docker-node/blob/master/docs/BestPractices.md#handling-kernel-signals
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