├── Dockerfile ├── LICENSE ├── README.md └── services ├── service1 ├── finish └── run └── service2 ├── finish └── run /Dockerfile: -------------------------------------------------------------------------------- 1 | FROM python:3-alpine 2 | 3 | RUN apk add --no-cache curl && \ 4 | curl --fail --silent -L https://github.com/just-containers/s6-overlay/releases/download/v1.21.8.0/s6-overlay-amd64.tar.gz | \ 5 | tar xzvf - -C / 6 | 7 | COPY ./services /etc/services.d/ 8 | ENTRYPOINT [ "/init" ] 9 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | 2 | Apache License 3 | Version 2.0, January 2004 4 | http://www.apache.org/licenses/ 5 | 6 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 7 | 8 | 1. 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This is where you decide 25 | whether the container should terminate when the service dies, or should `s6` 26 | restart the process. 27 | 28 | ### Review: example `run` script 29 | 30 | This script starts your service in the foreground (not like a daemon): 31 | 32 | ```sh 33 | #!/usr/bin/with-contenv sh 34 | echo >&2 "starting service1" 35 | exec python -m http.server "${PORT:-8080}" 36 | ``` 37 | 38 | Note we used `#!/usr/bin/with-contenv sh` (or `... bash`). This helps us 39 | [inherit environment variables][env] of the container. 40 | 41 | If you don't do that and do your usual 42 | `#!/bin/bash` (or even `#!/usr/bin/env bash`) etc, you will get fewer 43 | environment variables. (You can also run the container with `S6_KEEP_ENV=1` 44 | environment variable to avoid using `with-contenv`.) 45 | 46 | The `exec ...` command starts the long-running service process in the foreground 47 | and most importantly, `exec` **replaces the current shell process** so that 48 | our service is directly managed by `s6-supervise` (without `sh`/`bash` as its 49 | parent process). 50 | 51 | ### Review: example `finish` script 52 | 53 | This command gets the exit code of the `run` script as `$1` argument. When the 54 | service terminates, you can do either of these things 55 | 56 | - Terminate the container and kill the other service: see example below. 57 | - Have the service restarted by s6: either delete the `finish` script or don't 58 | use any commands like below that terminates the init process. 59 | 60 | ```sh 61 | #!/usr/bin/env sh 62 | echo >&2 "service1 exited. code=${1}" 63 | 64 | # terminate other services to exit from the container 65 | exec s6-svscanctl -t /var/run/s6/services 66 | ``` 67 | 68 | ## Try it out 69 | 70 | ```sh 71 | docker build -t test-image . 72 | docker run --rm -i -t --name=test test-image 73 | ``` 74 | 75 | On another terminal, run `docker exec test pstree` which will show the process 76 | tree inside the container with service1 (`python`) and service2 (`sleep`): 77 | 78 | ```text 79 | s6-svscan-+-s6-supervise 80 | |-s6-supervise---python 81 | `-s6-supervise---sleep 82 | ``` 83 | 84 | Similarly, you can send a graceful termination signal `SIGTERM` to the container 85 | and have both services terminate and their `finish` script runs: 86 | 87 | ```sh 88 | docker kill --signal=TERM test 89 | ``` 90 | 91 | ```text 92 | service1 exited. code=256 93 | service2 exited. code=256 94 | [cont-finish.d] executing container finish scripts... 95 | [cont-finish.d] done. 96 | [s6-finish] sending all processes the TERM signal. 97 | [s6-finish] sending all processes the KILL signal and exiting. 98 | ``` 99 | 100 | ## Learn more 101 | 102 | Hope you can use this sample to build containers that reliably run multiple 103 | processes in production. Remember, you should avoid doing this and split your 104 | processes into multiple containers as much as possible. 105 | 106 | You can learn more at [s6-overlay] repository which has a great user manual. The 107 | [s6] project page goes into more technical details. 108 | 109 | [s6-overlay]: https://github.com/just-containers/s6-overlay 110 | [s6]: https://skarnet.org/software/s6/ 111 | [init process]: https://en.wikipedia.org/wiki/Init 112 | [env]: https://github.com/just-containers/s6-overlay#container-environment 113 | -------------------------------------------------------------------------------- /services/service1/finish: -------------------------------------------------------------------------------- 1 | #!/usr/bin/env sh 2 | echo >&2 "service1 exited. code=${1}" 3 | 4 | # terminate other services to exit from the container 5 | exec s6-svscanctl -t /var/run/s6/services 6 | -------------------------------------------------------------------------------- /services/service1/run: -------------------------------------------------------------------------------- 1 | #!/usr/bin/with-contenv sh 2 | echo >&2 "starting service1" 3 | exec python -m http.server "${PORT:-8080}" 4 | -------------------------------------------------------------------------------- /services/service2/finish: -------------------------------------------------------------------------------- 1 | #!/usr/bin/env sh 2 | echo >&2 "service2 exited. code=${1}" 3 | 4 | # terminate other services to exit from the container 5 | exec s6-svscanctl -t /var/run/s6/services 6 | 7 | -------------------------------------------------------------------------------- /services/service2/run: -------------------------------------------------------------------------------- 1 | #!/usr/bin/with-contenv sh 2 | echo >&2 "starting service2" 3 | exec sleep 99999999 4 | --------------------------------------------------------------------------------