Prevent lambda timeouts or failure from not handled promise due to invalid SSM parameter(s)... Add throwOnFailedCall flag to the SSM middleware

packages/ssm/README.md

@@ -60,6 +60,7 @@ npm install --save @middy/ssm
   Defaults to `{ maxRetries: 6, retryDelayOptions: {base: 200} }`
 - `setToContext` (boolean) (optional): This will assign parameters to the `context` object
   of the function handler rather than to `process.env`. Defaults to `false`
+- `throwOnFailedCall` (boolean) (optional): Defaults to `false`. Set it to `true` if you want your lambda to fail in case call to AWS SSM fails (parameters don't exist or internal error). It will only print error if parameters are not already cached.
 
 NOTES:
 * While you don't need _both_ `paths` and `names`, you do need at least one of them!

packages/ssm/__tests__/index.js

@@ -292,7 +292,7 @@ describe('🔒 SSM Middleware', () => {
     })
   })
 
-  test('It should throw error when some SSM params are invalid', async () => {
+  test('It should throw error when some SSM params are invalid and "throwOnFailedCall" flag is set to true', async () => {
     await testScenario({
       ssmMockResponse: {
         InvalidParameters: ['invalid-smm-param-name', 'another-invalid-ssm-param']
@@ -301,7 +301,8 @@ describe('🔒 SSM Middleware', () => {
         names: {
           invalidParam: 'invalid-smm-param-name',
           anotherInvalidParam: 'another-invalid-ssm-param'
-        }
+        },
+        throwOnFailedCall: true
       },
       callbacks: [
         (error) => {
@@ -311,6 +312,31 @@ describe('🔒 SSM Middleware', () => {
     })
   })
 
+  test('It should resolve if "throwOnFailedCall" flag is not provided but some SSM params are invalid (will throw silently?)', async () => {
+    await testScenario({
+      ssmMockResponse: {
+        InvalidParameters: ['invalid-smm-param-name', 'another-invalid-ssm-param']
+      },
+      middlewareOptions: {
+        names: {
+          invalidParam: 'invalid-smm-param-name',
+          anotherInvalidParam: 'another-invalid-ssm-param'
+        },
+        throwOnFailedCall: false
+      },
+      callbacks: [
+        (_) => {
+          expect(_).toBeNull() // TODO: don't know how to test this properly... there is no mockObject to check whether was called or not! (Check if console.error prints '[Failed to get parameters from SSM] ...' ?)
+        },
+        () => {
+          expect(getParametersMock).toBeCalled()
+          expect(getParametersMock).toHaveBeenCalledTimes(2)
+          getParametersMock.mockClear()
+        }
+      ]
+    })
+  })
+
   test('It should not throw error when empty middleware params passed', async () => {
     await testScenario({
       ssmMockResponse: {},

packages/ssm/index.d.ts

@@ -8,6 +8,7 @@ interface ISSMOptions {
   paths?: { [key: string]: string; };
   names?: { [key: string]: string; };
   awsSdkOptions?: Partial<SSM.Types.ClientConfiguration>;
+  throwOnFailedCall?: boolean;
   setToContext?: boolean;
   paramsLoaded?: Boolean;
   getParamNameFromPath?: (path: string, name: string, prefix: string) => string;

packages/ssm/index.js

@@ -7,6 +7,7 @@ module.exports = opts => {
       maxRetries: 6, // lowers a chance to hit service rate limits, default is 3
       retryDelayOptions: { base: 200 }
     },
+    throwOnFailedCall: false,
     onChange: undefined,
     paths: {},
     names: {},
@@ -81,6 +82,22 @@ module.exports = opts => {
         options.paramsCache = objectsToMap
         options.paramsLoadedAt = new Date()
       })
+        .catch(err => {
+          console.error(
+            '[Failed to get parameters from SSM] ',
+            err.message
+          )
+          // throw error if there is no params in cache already and flag throwOnFailedCall is provided
+          if (options.throwOnFailedCall && !options.paramsCache) {
+            throw err
+          }
+          // if we already have a cached params, then reset the timestamp so we don't
+          // keep retrying on every invocation which can cause performance problems
+          // when there's temporary problems with SSM
+          if (options.paramsCache) {
+            options.paramsLoadedAt = new Date()
+          }
+        })
     }
   }
 }