Config files
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Config files let you provide file-shaped configuration to an app — for tools that insist on reading a path rather than an environment variable.
Use environment variables by default. Reach for a config file when a program genuinely requires one.
Adding one
On the app's Config Files panel, give the file a path inside the container and its contents. Saving restarts the app.
Typical uses:
- A tool's own configuration file —
server.yml,nginx.conf,config.toml - A CA bundle or certificate your app must read from disk
- A small seed or lookup file that never changes
They're mounted read-only
Your app can read a config file but cannot write to it. That's deliberate — it keeps the panel the single source of truth, so the file can't drift from what you think you configured.
The consequence to plan for: a tool that expects to rewrite its own config at runtime won't work this way. Those need a volume instead, with the trade-off that you then own the contents rather than the panel.
Some paths are off-limits
You can't mount over system paths — /proc, /sys, /dev, and the platform's own tooling directory are rejected. Put your files somewhere ordinary like /etc/myapp/ or /config/.
Config file or volume?
| You need | Use |
|---|---|
| Configuration you edit in the panel | Config file |
| Something the app writes to | Volume |
| A secret | Environment variable — or a config file if the tool demands a path |
| Anything large | Volume, or bake it into the image |
Config files are for small, hand-managed text. Anything the app manages itself belongs on a volume.
Secrets in config files
If a tool can only read credentials from a file, a config file is the right place — it's still part of the deployment rather than the image, so it isn't baked into a layer anyone who pulls the image can read.
Don't leave a copy in your repository as well. That's how the value ends up published.
Templates
Prefab templates can render parameters you supply into config files during deploy, which is how a ready-made app gets your settings without you editing anything by hand.