add docker compose section to multicontainer guide#2380
add docker compose section to multicontainer guide#2380
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Replace the nginx + custom-build rate-limiting example with a web service + Redis sidecar using two public images. The previous example referenced an nginx.conf and Dockerfile that weren't shown, so readers couldn't run it as written. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
fly deploy needs at least one Dockerfile, buildpack, or image in fly.toml to build from — a compose file with only pre-built images fails with "app does not have a Dockerfile or buildpacks configured." Add a minimal Dockerfile and switch the web service to build: . so the example is runnable as written. Also tighten the limitation wording from "only one" to "exactly one." Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
The example mapped container port 80 to host port 8080 in compose.yml and set internal_port = 8080 in fly.toml, but nginxdemos/hello listens on 80, so the Fly proxy forwarded traffic to a port nothing was listening on. Align everything on port 80. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
The [build.compose] block syntax was introduced in commit ee0ccdb (merged 2025-07-07 19:42 UTC), which first shipped in v0.3.152 (released 2025-07-08). v0.3.149-v0.3.151 only accept the older string-typed compose = "file.yml" field under [build] and reject the [build.compose] block with an unmarshal error. Verified by running fly config validate against each version. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
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LGTM! I tested it just to see it in action and confirm these instructions work - they do, out of the box.
Thanks!
Actually - EDIT: The compose file I used here specifies volumes, but flyctl will happily ignore volume setup it seems, and this will lead to data loss (imagine someone deploys paperless-ngx using that, writes a bunch of data to the rootfs and then restarts the machine).
We don't need to hold this doc update until we figure this out, but it would perhaps be good to point out somewhere that some compose configurations are recognized and handled by flyctl and some are happily ignored.
FWIW flyctl did say something about volumes at deploy time, but it's not super clear that this means "i'm not going to create or mount these volumes for you" - in principle it could not, because a Fly machine can only have one attached volume and this configuration wants 5 volumes.
$ fly deploy --ha=false
==> Verifying app config
Warning: Could not read volume file redisdata: open redisdata: no such file or directory
Warning: Could not read volume file data: open data: no such file or directory
Warning: Could not read volume file media: open media: no such file or directory
Warning: Could not read volume file export: open export: no such file or directory
Warning: Could not read volume file consume: open consume: no such file or directory
In summary, I think just a quick warning that if your compose file specifies volumes it will need adapting by hand might be worth it.
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Summary of changes
Add a self-contained section to add to the multi-container Machines guide. Covers config, routing, a practical nginx + Redis example, three clear limitations, and planned improvements.
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