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Advanced App Configuration

Service Update Override​

  • The Service Update Override field merges JSON or YAML settings into the Docker service update that CapRover prepares when an app is configured or deployed.
  • It is useful for Docker service options that the dashboard does not expose.
  • Start with the smallest possible override:
TaskTemplate:
  Resources:
    Limits:
      MemoryBytes: 104857600

  • This example limits the service to 100 MiB of memory.

  • Verify the value with docker service inspect SERVICE_NAME; obtain the actual name from docker service ls.

  • Test under realistic load before keeping a limit.

  • The update order is CapRover's normal settings, then the service override, then the optional pre-deploy function.

  • An override can replace a setting CapRover chose.

  • Values must match Docker's service update API.

  • Removing an override does not necessarily clear a Docker field that CapRover itself does not manage; explicitly reset the value when undoing such a change.

  • Keep a copy of the working service settings.

  • An invalid or contradictory override can block deployments.

  • See Docker's service update API for the schema used by the Docker version running your server.

Pre-Deploy Function​

  • A Pre-Deploy Function is JavaScript executed inside the CapRover process before an app's Docker service update.
  • It can inspect the stored app object and modify the service update object.
  • It runs after the standard app settings and Service Update Override have been applied.
var preDeployFunction = function (captainAppObj, dockerUpdateObject) {
  return Promise.resolve(dockerUpdateObject);
};

  • The function must return the service update object, possibly through a promise.

  • It executes again on deployments and configuration updates.

  • Test it against a disposable app before using it for important services, and preserve a working copy of the function and service configuration.

  • This code has the privileges of the CapRover process.

  • It can break service updates or access sensitive data, so restrict who can edit it.

  • For static service fields, prefer a Service Update Override.

  • Check docker service logs captain-captain if a service update fails before reaching Docker.