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.

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.