Feature request: add json schema to validate the daemon settings

[jdrouet]

Description

In docker cli, we already embed a json schema for docker compose, maybe we should have one also for the daemon settings.

Describe the results you expected:

Have a JSON Schema file with the settings definition

[thaJeztah]

This change would be in the moby repository (which is where the daemon CLI lives), but yes, I definitely agree we need something for this. From moby/moby#34093 (comment)

However (without having deep-dived into the code) I have a feeling we're reinventing the wheel; I think we're looking at properly validating the daemon.json; the format is currently "badly" documented (just the example JSON in https://docs.docker.com/engine/reference/commandline/dockerd/#daemon-configuration-file), which could use some improvement overall.

Would it be an idea to define a JSON schema for the configuration file, and use that for validating? Possibly we can use the schema itself to generate documentation as well (which would be a win-win)

Some related issues;

• Warn about unknown options in the config file  moby/moby#34093 ("warn for unknown options")
• How to check docker daemon options when using daemon.json moby/moby#21559 ("How to check docker daemon options when using daemon.json")
• Feature request: Make json files diffable moby/moby#34673 Feature request: Make json files diffable
  • Abandon: Add support to TOML format in configuration file moby/moby#34838 / Add support to TOML format in configuration file moby/moby#35640 Add support to TOML format in configuration file
• Use daemon.json in standard installs moby/moby#20151 Use daemon-config.json in standard installs
• Conflict between default -H fd:// systemd config and daemon.json hosts config moby/moby#25471 ("Conflict between default -H fd:// systemd config and daemon.json hosts config")
• Allow querying of daemon's log-driver and log-opt via remote API moby/moby#25508 ("Allow querying of daemon's log-driver and log-opt via remote API ")
• Dockerd needs a 'validate config' option moby/moby#36911 Dockerd needs a 'validate config' option
  • Add configuration validation option. moby/moby#38138 Add configuration validation option
• daemon.json parsing ignores unknown fields moby/moby#32530 ("daemon.json parsing ignores unknown fields")
  • Warn about unknown options in the config file  moby/moby#34093 Warn about unknown options in the config file
  • discusses JSON-schema as a possible approach; Warn about unknown options in the config file  moby/moby#34093 (comment)
• Add daemon option --default-shm-size moby/moby#29692 (comment) (Docker for Mac being out of sync with actual supported options)
• Generate compose file reference from JSON-schema #1058 Generate compose file reference from JSON-schema
  • s/compose file/daemon config/

[thaJeztah]

One thing to take into account is daemon upgrades/downgrades may invalidate existing configuration files; we should either "error", or "warn" on those

[jacobseth]

Hey there, could I have a go at this?

[thaJeztah]

@jcsirot did you already have a json-schema created? ^^

[jcsirot]

Well, I don't know. Maybe you wanted to ask @jdrouet :-D

[peter-curiousit]

For anyone like me looking for something to help write the daemon.json file, I found this: https://json.schemastore.org/dockerd.json

I'm not sure how accurate it is so YMMV