Transform SNS elements and move them to the alias stack.

README.md

@@ -115,6 +115,23 @@ automatically.
 Event subscriptions that are defined for a lambda function will be deployed per
 alias, i.e. the event will trigger the correct deployed aliased function.
 
+### SNS
+
+Subscriptions to SNS topics can be implicitly defined by adding an `sns` event to
+any existing lambda function definition. Serverless will create the topic for you
+and add a subscription to the deployed function.
+
+With the alias plugin the subscription will be per alias. Additionally the created
+topic is renamed and the alias name is added (e.g. myTopic-myAlias). This is done
+because SNS topics are independent per stage. Imagine you want to introduce a new
+topic or change the data/payload format of an existing one. Just attaching different
+aliases to one central topic would eventually break the system, as functions from
+different stages will receive the new data format. The topic-per-alias approach
+effectively solves the problem.
+
+If you want to refer to the topic programmatically, you just can add `-${process.env.SERVERLESS_ALIAS}`
+to the base topic name.
+
 ### Use with global resources
 
 Event subscriptions can reference resources that are available throughout all

lib/aliasRestructureStack.js

@@ -19,6 +19,7 @@ const userResources = require('./stackops/userResources');
 const lambdaRole = require('./stackops/lambdaRole');
 const events = require('./stackops/events');
 const cwEvents = require('./stackops/cwEvents');
+const snsEvents = require('./stackops/snsEvents');
 
 module.exports = {
 
@@ -50,6 +51,10 @@ module.exports = {
 		return cwEvents.call(this, currentTemplate, aliasStackTemplates, currentAliasStackTemplate);
 	},
 
+	aliasHandleSNSEvents(currentTemplate, aliasStackTemplates, currentAliasStackTemplate) {
+		return snsEvents.call(this, currentTemplate, aliasStackTemplates, currentAliasStackTemplate);
+	},
+
 	aliasFinalize(currentTemplate, aliasStackTemplates, currentAliasStackTemplate) {
 		const stageStack = this._serverless.service.provider.compiledCloudFormationTemplate;
 		const aliasStack = this._serverless.service.provider.compiledCloudFormationAliasTemplate;
@@ -84,6 +89,7 @@ module.exports = {
 		.spread(this.aliasHandleApiGateway)
 		.spread(this.aliasHandleEvents)
 		.spread(this.aliasHandleCWEvents)
+		.spread(this.aliasHandleSNSEvents)
 		.spread(this.aliasFinalize)
 		.then(() => BbPromise.resolve());
 	}

lib/stackops/snsEvents.js

@@ -0,0 +1,79 @@
+'use strict';
+
+/**
+ * Handle SNS Lambda subscriptions.
+ */
+
+const _ = require('lodash');
+const BbPromise = require('bluebird');
+const utils = require('../utils');
+
+module.exports = function(currentTemplate, aliasStackTemplates, currentAliasStackTemplate) {
+	const stageStack = this._serverless.service.provider.compiledCloudFormationTemplate;
+	const aliasStack = this._serverless.service.provider.compiledCloudFormationAliasTemplate;
+
+	this.options.verbose && this._serverless.cli.log('Processing SNS Lambda subscriptions');
+
+	const aliasResources = [];
+
+	const aliases = _.assign({}, _.pickBy(aliasStack.Resources, [ 'Type', 'AWS::Lambda::Alias' ]));
+	const versions = _.assign({}, _.pickBy(aliasStack.Resources, [ 'Type', 'AWS::Lambda::Version' ]));
+
+	// Add alias name to topics to disambiguate behavior
+	const snsTopics =
+			_.assign({},
+				_.pickBy(stageStack.Resources, [ 'Type', 'AWS::SNS::Topic' ]));
+
+	_.forOwn(snsTopics, (topic, name) => {
+		topic.DependsOn = topic.DependsOn || [];
+		// Remap lambda subscriptions
+		const lambdaSubscriptions = _.pickBy(topic.Properties.Subscription, ['Protocol', 'lambda']);
+		_.forOwn(lambdaSubscriptions, subscription => {
+			const functionNameRef = utils.findAllReferences(_.get(subscription, 'Endpoint'));
+			const functionName = _.replace(_.get(functionNameRef, '[0].ref', ''), /LambdaFunction$/, '');
+			const versionName = _.find(_.keys(versions), version => _.startsWith(version, functionName));
+			const aliasName = _.find(_.keys(aliases), alias => _.startsWith(alias, functionName));
+
+			subscription.Endpoint = { Ref: aliasName };
+
+			// Add dependency on function version
+			topic.DependsOn.push(versionName);
+			topic.DependsOn.push(aliasName);
+		});
+
+		topic.Properties.TopicName = `${topic.Properties.TopicName}-${this._alias}`;
+
+		delete stageStack.Resources[name];
+	});
+
+	// Fetch lambda permissions. These have to be updated later to allow the aliased functions.
+	const snsLambdaPermissions =
+			_.assign({},
+				_.pickBy(_.pickBy(stageStack.Resources, [ 'Type', 'AWS::Lambda::Permission' ]),
+				[ 'Properties.Principal', 'sns.amazonaws.com' ]));
+
+	// Adjust permission to reference the function aliases
+	_.forOwn(snsLambdaPermissions, (permission, name) => {
+		const functionName = _.replace(name, /LambdaPermission.*$/, '');
+		const versionName = _.find(_.keys(versions), version => _.startsWith(version, functionName));
+		const aliasName = _.find(_.keys(aliases), alias => _.startsWith(alias, functionName));
+
+		// Adjust references and alias permissions
+		permission.Properties.FunctionName = { Ref: aliasName };
+		const sourceArn = _.get(permission.Properties, 'SourceArn.Fn::Join[1]', []);
+		sourceArn.push(`-${this._alias}`);
+
+		// Add dependency on function version
+		permission.DependsOn = [ versionName, aliasName ];
+
+		delete stageStack.Resources[name];
+	});
+
+	// Add all alias stack owned resources
+	aliasResources.push(snsTopics);
+	aliasResources.push(snsLambdaPermissions);
+
+	_.forEach(aliasResources, resource => _.assign(aliasStack.Resources, resource));
+
+	return BbPromise.resolve([ currentTemplate, aliasStackTemplates, currentAliasStackTemplate ]);
+};

test/aliasRestructureStack.test.js

@@ -91,6 +91,7 @@ describe('aliasRestructureStack', () => {
 			const aliasHandleApiGatewaySpy = sandbox.spy(awsAlias, 'aliasHandleApiGateway');
 			const aliasHandleEventsSpy = sandbox.spy(awsAlias, 'aliasHandleEvents');
 			const aliasHandleCWEventsSpy = sandbox.spy(awsAlias, 'aliasHandleCWEvents');
+			const aliasHandleSNSEventsSpy = sandbox.spy(awsAlias, 'aliasHandleSNSEvents');
 			const aliasFinalizeSpy = sandbox.spy(awsAlias, 'aliasFinalize');
 
 			const currentTemplate = require('./data/sls-stack-2.json');
@@ -107,6 +108,7 @@ describe('aliasRestructureStack', () => {
 				expect(aliasHandleApiGatewaySpy).to.have.been.calledWithExactly(currentTemplate, [ aliasTemplate ], currentAliasStackTemplate),
 				expect(aliasHandleEventsSpy).to.have.been.calledWithExactly(currentTemplate, [ aliasTemplate ], currentAliasStackTemplate),
 				expect(aliasHandleCWEventsSpy).to.have.been.calledWithExactly(currentTemplate, [ aliasTemplate ], currentAliasStackTemplate),
+				expect(aliasHandleSNSEventsSpy).to.have.been.calledWithExactly(currentTemplate, [ aliasTemplate ], currentAliasStackTemplate),
 				expect(aliasFinalizeSpy).to.have.been.calledWithExactly(currentTemplate, [ aliasTemplate ], currentAliasStackTemplate),
 			]));
 		});