Initial implementation of TechDocs cache in backend plugin

Signed-off-by: Eric Peterson <ericpeterson@spotify.com>

plugins/techdocs-backend/config.d.ts

@@ -226,6 +226,23 @@ export interface Config {
           };
         };
 
+    /**
+     * @example http://localhost:7007/api/techdocs
+     * Techdocs cache information
+     */
+    cache?: {
+      /**
+       * The cache time-to-live for TechDocs sites (in milliseconds). Set this
+       * to a non-zero value to cache TechDocs sites and assets as they are
+       * read from storage.
+       *
+       * Note: you must also configure `backend.cache` appropriately as well,
+       * and to pass a PluginCacheManager instance to TechDocs Backend's
+       * createRouter method in your backend.
+       */
+      ttl: number;
+    };
+
     /**
      * @example http://localhost:7007/api/techdocs
      * @visibility frontend

plugins/techdocs-backend/src/DocsBuilder/builder.ts

@@ -36,6 +36,7 @@ import path from 'path';
 import { Writable } from 'stream';
 import { Logger } from 'winston';
 import { BuildMetadataStorage } from './BuildMetadataStorage';
+import { TechDocsCache } from '../cache';
 
 type DocsBuilderArguments = {
   preparers: PreparerBuilder;
@@ -46,6 +47,7 @@ type DocsBuilderArguments = {
   config: Config;
   scmIntegrations: ScmIntegrationRegistry;
   logStream?: Writable;
+  cache?: TechDocsCache;
 };
 
 export class DocsBuilder {
@@ -57,6 +59,7 @@ export class DocsBuilder {
   private config: Config;
   private scmIntegrations: ScmIntegrationRegistry;
   private logStream: Writable | undefined;
+  private cache?: TechDocsCache;
 
   constructor({
     preparers,
@@ -67,6 +70,7 @@ export class DocsBuilder {
     config,
     scmIntegrations,
     logStream,
+    cache,
   }: DocsBuilderArguments) {
     this.preparer = preparers.get(entity);
     this.generator = generators.get(entity);
@@ -76,6 +80,7 @@ export class DocsBuilder {
     this.config = config;
     this.scmIntegrations = scmIntegrations;
     this.logStream = logStream;
+    this.cache = cache;
   }
 
   /**
@@ -210,11 +215,16 @@ export class DocsBuilder {
       )}`,
     );
 
-    await this.publisher.publish({
+    const published = await this.publisher.publish({
       entity: this.entity,
       directory: outputDir,
     });
 
+    // Invalidate the cache for any published objects.
+    if (this.cache && published?.objects?.length) {
+      await this.cache.invalidateMultiple(published.objects);
+    }
+
     try {
       // Not a blocker hence no need to await this.
       fs.remove(outputDir);

plugins/techdocs-backend/src/service/router.ts

@@ -13,7 +13,10 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { PluginEndpointDiscovery } from '@backstage/backend-common';
+import {
+  PluginEndpointDiscovery,
+  PluginCacheManager,
+} from '@backstage/backend-common';
 import { CatalogClient } from '@backstage/catalog-client';
 import { Entity, stringifyEntityRef } from '@backstage/catalog-model';
 import { Config } from '@backstage/config';
@@ -31,6 +34,7 @@ import { Knex } from 'knex';
 import { Logger } from 'winston';
 import { ScmIntegrations } from '@backstage/integration';
 import { DocsSynchronizer, DocsSynchronizerSyncOpts } from './DocsSynchronizer';
+import { createCacheMiddleware, TechDocsCache } from '../cache';
 
 /**
  * All of the required dependencies for running TechDocs in the "out-of-the-box"
@@ -44,6 +48,7 @@ type OutOfTheBoxDeploymentOptions = {
   discovery: PluginEndpointDiscovery;
   database?: Knex; // TODO: Make database required when we're implementing database stuff.
   config: Config;
+  cache?: PluginCacheManager;
 };
 
 /**
@@ -88,6 +93,14 @@ export async function createRouter(
     scmIntegrations,
   });
 
+  // Set up a cache client if configured.
+  let cache: TechDocsCache | undefined;
+  const defaultTtl = config.getOptionalNumber('techdocs.cache.ttl');
+  if (isOutOfTheBoxOption(options) && options.cache && defaultTtl) {
+    const cacheClient = options.cache.getClient({ defaultTtl });
+    cache = new TechDocsCache({ cache: cacheClient, logger });
+  }
+
   router.get('/metadata/techdocs/:namespace/:kind/:name', async (req, res) => {
     const { kind, namespace, name } = req.params;
     const entityName = { kind, namespace, name };
@@ -199,6 +212,11 @@ export async function createRouter(
     );
   });
 
+  // If a cache manager was provided, attach the cache middleware.
+  if (cache) {
+    router.use(createCacheMiddleware({ logger, cache }));
+  }
+
   // Route middleware which serves files from the storage set in the publisher.
   router.use('/static/docs', publisher.docsRouter());