feat: Implement HealthCheck functionality

src/Service/BaseConfig.service.js

@@ -1,7 +1,7 @@
 import { S3 } from 'aws-sdk';
 
 import DependencyAwareClass from '../DependencyInjection/DependencyAware.class';
-
+import LambdaTermination from '../Wrapper/LambdaTermination';
 /**
  * Error.code for S3 404 errors
  */
@@ -16,6 +16,15 @@ export const ServiceStates = {
   INDEFINITELY_PAUSED: 'UNDEFINITELY_PAUSED',
 };
 
+/**
+ * Maps service states to HTTP codes
+ */
+export const ServiceStatesHttpCodes = {
+  [ServiceStates.OK]: 200,
+  [ServiceStates.TEMPORARY_PAUSED]: 409,
+  [ServiceStates.INDEFINITELY_PAUSED]: 409,
+};
+
 /**
  * BaseConfigService class
  *
@@ -159,4 +168,37 @@ export default class BaseConfigService extends DependencyAwareClass {
       ...partialConfig,
     });
   }
+
+  /**
+   * Performs a health check
+   * given the currentConfig.
+   *
+   * If currentConfig is not supplied
+   * it uses `getOrCreate` to fetch it.
+   *
+   * @param currentConfig
+   */
+  async healthCheck(currentConfig = null) {
+    const config = currentConfig || await this.getOrCreate();
+
+    return ServiceStatesHttpCodes[config.state] || 500;
+  }
+
+  /**
+   * Ensures that the application is healthy
+   * or throws a LambdaTermination
+   *
+   * @param currentConfig
+   */
+  async ensureHealthy(currentConfig = null) {
+    const statusCode = await this.healthCheck(currentConfig);
+
+    if (statusCode < 400) {
+      return statusCode;
+    }
+
+    const message = 'Application is not healthy.';
+
+    throw new LambdaTermination(message, statusCode, message, message);
+  }
 }

tests/unit/Service/BaseConfig.service.test.js

@@ -1,7 +1,7 @@
 import { S3 } from 'aws-sdk';
 
 import DependencyInjection from '../../../src/DependencyInjection/DependencyInjection.class';
-import BaseConfigService, { S3_NO_SUCH_KEY_ERROR_CODE } from '../../../src/Service/BaseConfig.service';
+import BaseConfigService, { S3_NO_SUCH_KEY_ERROR_CODE, ServiceStates, ServiceStatesHttpCodes } from '../../../src/Service/BaseConfig.service';
 
 const createAsyncMock = (returnValue) => {
   const mockedValue = returnValue instanceof Error
@@ -182,6 +182,74 @@ const BaseConfigUnitTests = (serviceGenerator: (...args) => BaseConfigService) =
       await expect(service.patch({ b: 1 })).rejects.toThrowErrorMatchingSnapshot();
     });
   });
+
+  describe('healthCheck', () => {
+    Object.values(ServiceStates).forEach((state) => {
+      describe(state, () => {
+        it('Returns the expected HTTP code with the given config', async () => {
+          const config = { state };
+          const service = serviceGenerator();
+          const statusCode = await service.healthCheck(config);
+          const expected = ServiceStatesHttpCodes[state];
+
+          expect(statusCode).toEqual(expected);
+        });
+
+        it('Returns the expected HTTP code with the existing config', async () => {
+          const config = { state };
+          const service = serviceGenerator({ getObject: { Body: JSON.stringify(config) } });
+          const statusCode = await service.healthCheck();
+          const expected = ServiceStatesHttpCodes[state];
+
+          expect(statusCode).toEqual(expected);
+        });
+      });
+    });
+
+    describe('Unknown state', () => {
+      it('Returns 500 with the given config', async () => {
+        const config = { state: 'Unknown' };
+        const service = serviceGenerator();
+        const statusCode = await service.healthCheck(config);
+        const expected = 500;
+
+        expect(statusCode).toEqual(expected);
+      });
+
+      it('Returns 500 with the existing config', async () => {
+        const config = { state: 'Unknown' };
+        const service = serviceGenerator({ getObject: { Body: JSON.stringify(config) } });
+        const statusCode = await service.healthCheck();
+        const expected = 500;
+
+        expect(statusCode).toEqual(expected);
+      });
+    });
+  });
+
+  describe('ensureHealthy', () => {
+    [200, 201, 202, 204, 300, 301, 399].forEach((statusCode) => {
+      describe(statusCode, () => {
+        it('is healthy', async () => {
+          const service = serviceGenerator();
+          jest.spyOn(service, 'healthCheck').mockImplementation(() => Promise.resolve(statusCode));
+
+          await expect(service.ensureHealthy()).resolves.toEqual(statusCode);
+        });
+      });
+    });
+
+    [400, 401, 403, 404, 409, 499, 500, 501, 502, 503, 504, 'Dante Alighieri'].forEach((statusCode) => {
+      describe(statusCode, () => {
+        it('throws a LambdaTermination', async () => {
+          const service = serviceGenerator();
+          jest.spyOn(service, 'healthCheck').mockImplementation(() => Promise.resolve(statusCode));
+
+          await expect(service.ensureHealthy()).rejects.toThrowErrorMatchingSnapshot();
+        });
+      });
+    });
+  });
 };
 
 describe('Service/BaseConfigService', () => {

tests/unit/Service/__snapshots__/BaseConfig.service.test.js.snap

@@ -1,5 +1,29 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`Service/BaseConfigService ensureHealthy 400 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 401 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 403 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 404 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 409 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 499 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 500 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 501 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 502 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 503 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy 504 throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
+exports[`Service/BaseConfigService ensureHealthy Dante Alighieri throws a LambdaTermination 1`] = `"Application is not healthy."`;
+
 exports[`Service/BaseConfigService get propagates the 404 1`] = `"404"`;
 
 exports[`Service/BaseConfigService get refuses empty configurations 1`] = `"Configuration file is empty"`;