Merge pull request #9225 from RoadieHQ/softer-proxy-startup

allow backend to start if proxy target is not set

.changeset/quick-jars-wait.md

@@ -0,0 +1,26 @@
+---
+'@backstage/plugin-proxy-backend': patch
+---
+
+Adds a new option `skipInvalidTargets` for the proxy `createRouter` which allows the proxy backend to be started with an invalid proxy configuration. If configured, it will simply skip the failed proxy and mount the other valid proxies.
+
+To configure it to pass by failing proxies:
+
+```
+const router = await createRouter({
+  config,
+  logger,
+  discovery,
+  skipInvalidProxies: true,
+});
+```
+
+If you would like it to fail if a proxy is configured badly:
+
+```
+const router = await createRouter({
+  config,
+  logger,
+  discovery,
+});
+```

plugins/proxy-backend/src/service/router.test.ts

@@ -30,23 +30,96 @@ const mockCreateProxyMiddleware = createProxyMiddleware as jest.MockedFunction<
 >;
 
 describe('createRouter', () => {
-  it('works', async () => {
-    const logger = getVoidLogger();
-    const config = new ConfigReader({
-      backend: {
-        baseUrl: 'https://example.com:7007',
-        listen: {
-          port: 7007,
+  describe('where all proxy config are valid', () => {
+    it('works', async () => {
+      const logger = getVoidLogger();
+      const config = new ConfigReader({
+        backend: {
+          baseUrl: 'https://example.com:7007',
+          listen: {
+            port: 7007,
+          },
         },
-      },
+        proxy: {
+          '/test': {
+            target: 'https://example.com',
+            headers: {
+              Authorization: 'Bearer supersecret',
+            },
+          },
+        },
+      });
+      const discovery = SingleHostDiscovery.fromConfig(config);
+      const router = await createRouter({
+        config,
+        logger,
+        discovery,
+      });
+      expect(router).toBeDefined();
     });
-    const discovery = SingleHostDiscovery.fromConfig(config);
-    const router = await createRouter({
-      config,
-      logger,
-      discovery,
+  });
+
+  describe('where buildMiddleware would fail', () => {
+    it('throws an error if skip failures is not set', async () => {
+      const logger = getVoidLogger();
+      logger.warn = jest.fn();
+      const config = new ConfigReader({
+        backend: {
+          baseUrl: 'https://example.com:7007',
+          listen: {
+            port: 7007,
+          },
+        },
+        // no target would cause the buildMiddleware to fail
+        proxy: {
+          '/test': {
+            headers: {
+              Authorization: 'Bearer supersecret',
+            },
+          },
+        },
+      });
+      const discovery = SingleHostDiscovery.fromConfig(config);
+      await expect(
+        createRouter({
+          config,
+          logger,
+          discovery,
+        }),
+      ).rejects.toThrow(new Error('Proxy target must be a string'));
+    });
+
+    it('works if skip failures is set', async () => {
+      const logger = getVoidLogger();
+      logger.warn = jest.fn();
+      const config = new ConfigReader({
+        backend: {
+          baseUrl: 'https://example.com:7007',
+          listen: {
+            port: 7007,
+          },
+        },
+        // no target would cause the buildMiddleware to fail
+        proxy: {
+          '/test': {
+            headers: {
+              Authorization: 'Bearer supersecret',
+            },
+          },
+        },
+      });
+      const discovery = SingleHostDiscovery.fromConfig(config);
+      const router = await createRouter({
+        config,
+        logger,
+        discovery,
+        skipInvalidProxies: true,
+      });
+      expect((logger.warn as jest.Mock).mock.calls[0][0]).toEqual(
+        'skipped configuring /test due to Proxy target must be a string',
+      );
+      expect(router).toBeDefined();
     });
-    expect(router).toBeDefined();
   });
 });
 

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

@@ -51,6 +51,7 @@ export interface RouterOptions {
   logger: Logger;
   config: Config;
   discovery: PluginEndpointDiscovery;
+  skipInvalidProxies?: boolean;
 }
 
 export interface ProxyConfig extends Options {
@@ -185,11 +186,20 @@ export async function createRouter(
   const { pathname: pathPrefix } = new URL(externalUrl);
 
   const proxyConfig = options.config.getOptional('proxy') ?? {};
+
   Object.entries(proxyConfig).forEach(([route, proxyRouteConfig]) => {
-    router.use(
-      route,
-      buildMiddleware(pathPrefix, options.logger, route, proxyRouteConfig),
-    );
+    try {
+      router.use(
+        route,
+        buildMiddleware(pathPrefix, options.logger, route, proxyRouteConfig),
+      );
+    } catch (e) {
+      if (options.skipInvalidProxies) {
+        options.logger.warn(`skipped configuring ${route} due to ${e.message}`);
+      } else {
+        throw e;
+      }
+    }
   });
 
   return router;