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82 lines
2.6 KiB
Markdown
82 lines
2.6 KiB
Markdown
# Shutdown gracefully
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<br/><br/>
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### One Paragraph Explainer
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In a Dockerized runtime like Kubernetes, containers are born and die frequently. This happens not only when errors are thrown but also for good reasons like relocating containers, replacing them with a newer version and more. It's achieved by sending a notice (SIGTERM signal) to the process with a 30 second grace period. This puts a challenge on the developer to ensure the app is handling the ongoing requests and clean-up resources in a timely fashion. Otherwise thousands of sad users will not get a response. Implementation-wise, the shutdown code should wait until all ongoing requests are flushed out and then clean-up resources. Easier said than done, practically it demands orchestrating several parts: Tell the LoadBalancer that the app is not ready to serve more requests (via health-check), wait for existing requests to be done, avoid handling new requests, clean-up resources and finally log some useful information before dying. If Keep-Alive connections are being used, the clients must also be notified that a new connection should be established - A library like [Stoppable](https://github.com/hunterloftis/stoppable) can greatly help achieving this.
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<br/><br/>
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### Code Example – Placing Node.js as the root process allows passing signals to the code (see [bootstrap using node](./bootstrap-using-node.md))
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<details>
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<summary><strong>Dockerfile</strong></summary>
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```dockerfile
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FROM node:12-slim
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# Build logic comes here
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CMD ["node", "index.js"]
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#This line above will make Node.js the root process (PID1)
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```
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</details>
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<br/><br/>
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### Code Example – Using Tiny process manager to forward signals to Node
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<details>
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<summary><strong>Dockerfile</strong></summary>
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```dockerfile
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FROM node:12-slim
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# Build logic comes here
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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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ENTRYPOINT ["/tini", "--"]
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CMD ["node", "index.js"]
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#Now Node will run a sub-process of TINI which acts as PID1
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```
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</details>
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<br/><br/>
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### Code Example Anti Pattern – Using npm scripts to initialize the process
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<details>
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<summary><strong>Dockerfile</strong></summary>
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```dockerfile
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FROM node:12-slim
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# Build logic comes here
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CMD ["npm", "start"]
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#Now Node will run a sub-process of npm and won't receive signals
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```
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</details>
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<br/><br/>
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### Example - The shutdown phases
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From the blog, [Rising Stack](https://blog.risingstack.com/graceful-shutdown-node-js-kubernetes/)
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