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Catalog Configuration

Processors​

The catalog has a concept of processors to perform catalog ingestion tasks, such as reading raw entity data from a remote source, parsing it, transforming it, and validating it. These processors are configured under the catalog.processors configuration key.

Static Location Configuration​

The simplest configuration for the catalog, as shown in the default @backstage/create-app template, is to declaratively add locations pointing to YAML files with static configuration.

Locations are added to the catalog under the catalog.locations key:

catalog:
  locations:
    - type: url
      target: https://github.com/backstage/backstage/blob/master/packages/catalog-model/examples/components/artist-lookup-component.yaml

The url type locations are handled by a standard processor included with the catalog (UrlReaderProcessor), so no processor configuration is needed. This processor does however need an integration to understand how to retrieve a given URL. For the example above, you would need to configure the GitHub integration to read files from github.com.

The locations added through static configuration cannot be removed through the catalog locations API. To remove these locations, you must remove them from the configuration.

Syntax errors or other types of errors present in catalog-info.yaml files will be logged for investigation. Errors do not cause processing to abort.

When multiple catalog-info.yaml files with the same metadata.name property are discovered, one will be processed and all others will be skipped. This action is logged for further investigation.

Local File (type: file) Configurations​

In addition to url locations, you can use the file location type to bring in content from the local file system. You should only use this for local development, test setups, and example data, not for production data. You are also not able to use placeholders in them like $text, $json or $yaml. You can however reference other files relative to the current file. See the full catalog example data set here for an extensive example.

Here is an example pulling in the all.yaml file from the examples folder. Note the use of ../../ to go up two levels from the current execution path of the backend. This is typically packages/backend/.

catalog:
  locations:
    - type: file
      target: ../../examples/all.yaml
note

There might be cases where you need to test some file configurations in a Docker container. In a case like this, as the backend is serving the frontend in a default setup, the path would be from the root. Also, you need to make sure to copy your files into your container.

Using the example above that would look like this:

catalog:
  locations:
    - type: file
      target: ./examples/all.yaml

Integration Processors​

Integrations may simply provide a mechanism to handle url location type for an external provider or they may also include additional processors out of the box, such as the GitHub discovery processor that scans a GitHub organization for entity descriptor files.

Check the integrations documentation to see what is offered by each integration.

Custom Processors​

To ingest entities from an existing system already tracking software, you can also write a custom processor to convert between the existing system and Backstage's descriptor format. This is documented in External Integrations.

Catalog Rules​

By default, the catalog will only allow the ingestion of entities with the kind Component, API, and Location. In order to allow entities of other kinds to be added, you need to add rules to the catalog. Rules are added either in a separate catalog.rules key or added to statically configured locations.

For example, given the following configuration:

catalog:
  rules:
    - allow: [Component, API, Location, Template]

  locations:
    - type: url
      target: https://github.com/org/example/blob/master/org-data.yaml
      rules:
        - allow: [Group]

We are able to add entities of kind Component, API, Location, or Template from any location, and Group entities from the org-data.yaml, which will also be read as a statically configured location.

Note that if the catalog.rules key is present it will replace the default value, meaning that you need to add rules for the default kinds if you want those to still be allowed.

The following configuration will reject any kind of entities from being added to the catalog:

catalog:
  rules: []

Readonly mode​

Processors provide a good way to automate the ingestion of entities when combined with Static Location Configuration or a discovery processor like GitHub Discovery. To enforce the usage of processors to locate entities we can configure the catalog into readonly mode. This configuration disables registering and deleting locations with the catalog APIs.

catalog:
  readonly: true

Note that any plugin relying on the catalog API for creating, updating, and deleting entities will not work in this mode.

Deleting an entity by UUID, DELETE /entities/by-uid/:uid, is allowed when using this mode. It may be rediscovered as noted in explicit deletion.

A common use case for this configuration is when organizations have a remote source that should be mirrored into Backstage. To make Backstage a mirror of this remote source, users cannot also register new entities with e.g. the catalog-import plugin.

Clean up orphaned entities​

In short, entities can become orphaned through multiple means, such as when a catalog-info YAML file is moved from one place to another in the version control system without updating the registration in the catalog. For safety reasons, the default behavior is to just tag the orphaned entities, and keep them around. You can read more about orphaned entities here.

However, if you do wish to automatically remove the orphaned entities, you can use the following configuration, and everything with an orphaned entity tag will be eventually deleted.

catalog:
  orphanStrategy: delete

Processing Interval​

The processing loop is responsible for running your registered processors on all entities, on a certain interval. That interval can be configured with the processingInterval app-config parameter.

catalog:
  processingInterval: { minutes: 45 }

The value is a duration object, that has one or more of the fields years, months, weeks, days, hours, minutes, seconds, and milliseconds. You can combine them, for example as { hours: 1, minutes: 15 } which essentially means that you want the processing loop to visit entities roughly once every 75 minutes.

Note that this is only a suggested minimum, and the actual interval may be longer. Internally, the catalog will scale up this number by a small factor and choose random numbers in that range to spread out the load. If the catalog is overloaded and cannot process all entities during the interval, the time taken between processing runs of any given entity may also be longer than specified here.

Setting this value too low risks exhausting rate limits on external systems that are queried by processors, such as version control systems housing catalog-info files.

Stitching strategy​

Stitching finalizes the entity. It can be run in two modes:

  • immediate - performs stitching in-band immediately when needed
  • deferred - performs the stitching asynchronously

It can be configured with the stitchingStrategy app-config parameter.

app-config.yaml
catalog:
  stitchingStrategy:
    mode: immediate

For the deferred mode you can set up additional parameters to further tune the process, by setting the following parameters:

  • pollingInterval - the interval between polling for entities that need stitching
  • stitchTimeout - the maximum time to wait for an entity to be stitched

These parameters accept a duration object, similar to the processingInterval parameter.

app-config.yaml
catalog:
  stitchingStrategy:
    mode: deferred
    pollingInterval: { seconds: 1 }
    stitchTimeout: { minutes: 1 };

Subscribing to Catalog Errors​

Catalog errors are published to the events plugin: @backstage/plugin-events-node. You can subscribe to events and respond to errors, for example you may wish to log them.

The first step is to add the events backend plugin to your Backstage application. Navigate to your Backstage application directory and add the plugin package.

From your Backstage root directory
yarn --cwd packages/backend add @backstage/plugin-events-backend

Now you can install the events backend plugin in your backend.

packages/backend/src/index.ts
backend.add(import('@backstage/plugin-events-backend'));

Logging Errors​

If you want to log catalog errors you can install the @backstage/plugin-catalog-backend-module-logs module.

Install the catalog logs module.

From your Backstage root directory
yarn --cwd packages/backend add @backstage/plugin-catalog-backend-module-logs

Add the module to your backend.

packages/backend/src/index.ts
backend.add(import('@backstage/plugin-catalog-backend-module-logs'));

This will log errors with a level of warn.

You should now see logs as the catalog emits events. Example:

[1] 2024-06-07T00:00:28.787Z events warn Policy check failed for user:default/guest; caused by Error: Malformed envelope, /metadata/tags must be array entity=user:default/guest location=file:/Users/foobar/code/backstage-demo-instance/examples/org.yaml

Custom Error Handling​

If you wish to handle catalog errors with specific logic different from logging the errors the following should help you get started. For example, you may wish to send a notification or create a ticket for someone to investigate.

Create a backend module that subscribes to the catalog error events. The topic is experimental.catalog.errors.

packages/backend/src/index.ts
import { CATALOG_ERRORS_TOPIC } from '@backstage/plugin-catalog-backend';
import {
  coreServices,
  createBackendModule,
} from '@backstage/backend-plugin-api';
import { eventsServiceRef, EventParams } from '@backstage/plugin-events-node';

interface EventsPayload {
  entity: string;
  location?: string;
  errors: Error[];
}

interface EventsParamsWithPayload extends EventParams {
  eventPayload: EventsPayload;
}

const eventsModuleCatalogErrors = createBackendModule({
  pluginId: 'events',
  moduleId: 'catalog-errors',
  register(env) {
    env.registerInit({
      deps: {
        events: eventsServiceRef,
        logger: coreServices.logger,
      },
      async init({ events, logger }) {
        events.subscribe({
          id: 'catalog',
          topics: [CATALOG_ERRORS_TOPIC],
          async onEvent(params: EventParams): Promise<void> {
            const event = params as EventsParamsWithPayload;
            const { entity, location, errors } = event.eventPayload;
            // Add custom logic here for responding to errors
            for (const error of errors) {
              logger.warn(error.message, {
                entity,
                location,
              });
            }
          },
        });
      },
    });
  },
});

Now install your module.

packages/backend/src/index.ts
backend.add(eventsModuleCatalogErrors);