How to Add a Cache Layer to Serverless GraphQL AppSync API

In this post, I show an example of simple application based on the . The application uses Amazon Appsync, Lambda, DynamoDB, , to demonstrate how to use Amazon DAX as caching layer in front of AWS Appsync Resolvers. Serverless framework Amazon DynamoDB Accelerator (DAX) Amazon DynamoDB Accelerator (DAX) is a fully managed, highly available, in-memory for that delivers up to a 10x performance improvement — from milliseconds to microseconds — even at millions of requests per second. cache DynamoDB A simple serverless CMS The example application in this post is a simple CMS. I use Serverless framework templates to simplify the setup for Appsync. The sections in template that create the Appsync, Dynamodb, Cognito identity pool and user pool, DAX cluster, roles, security groups, and subnet groups, and you can use them for automatic and repeatable deployments. The following diagram illustrates application solution: Getting started with Serverless Framework To start, you need to have the Serverless Framework installed: $ npm install -g serverless Now, let’s create a new serverless project: $ sls create --template aws-nodejs --path simpleCMS $ cd simpleCMS $ npm init The directory that is created includes two files — handler.js is the Lambda function. The serverless.yml file contains the configurations of the backend. Add Plugins You need to add two plugins of Serverless framework: and : serverless-appsync-plugin serverless-pseudo-parameters $ npm install serverless-pseudo-parameters $ npm install serverless-appsync-plugin Edit the serverless.yml file and add the plugins to section: plugins plugins: - serverless-appsync-plugin - serverless-pseudo-parameters Define the AWS AppSync Schema Let’s look at the schema. Schema files are text files, usually named schema.graphql, the sample scheme should look like as below: https://medium.com/media/5cf9c8c080c05375eb1fd89c8c6f206c/href Create Mapping Templates Now we have our schema defined we need to add resolvers for it, The mapping template files should be located in a directory called mapping-templates relative to the serverless.yml file. Pipeline resolvers AppSync team released resolvers last year, Pipeline resolvers offer the ability to serially execute operations against data sources. pipeline In this example, there are two functions attached Query and Mutation APIs , The pipeline resolver to run the following logic: Connect to the Lambda datasource, get/put item from/to DAX. If the Lambda function raises an error, connect to DynamoDb datasource, get/put item from/to DynamoDb directly. Let’s create the request template for adding post mutation in a file called mapping-templates/Mutation-addPost-request.vtl , note that it is a resolver. It will save the argument to context stash and invoke the attached pipeline functions. pipeline $util.qr($context.stash.put("id", $util.autoId())) $util.qr($context.stash.put("title", $ctx.args.post.title)) $util.qr($context.stash.put("createdAt", $util.time.nowISO8601())) $util.qr($context.stash.put("content", $ctx.args.post.content)) {} Then create template for the first pipeline function mapping-templates/Function-addPostViaDax-request.vtl which will invoke a lambda function to insert post to . DAX { "version": "2017-02-28", "operation": "Invoke", "payload": { "field": "addPostViaDax", "arguments": $utils.toJson($context.stash) } } Next let’s create the second pipeline function template mapping-templates/Function-addPostToDB-request.vtl which will insert post to DynamoDB directly if previous lambda function execrated failed. #if($ctx.prev.result.errorMessage) { "version" : "2017-02-28", "operation" : "PutItem", "key": { "id" : $util.dynamodb.toDynamoDBJson($context.stash.id) }, "attributeValues" : { "title" : $util.dynamodb.toDynamoDBJson($context.stash.title) , "content" : $util.dynamodb.toDynamoDBJson($context.stash.content), "createdAt": $util.dynamodb.toDynamoDBJson($context.stash.createdAt) }, } #else #return($ctx.prev.result) #end Define Dependent Services Now, I need a DynamoDB table, Appsync, Amazon Cognito user pool and identity pool, DAX in a Vpc, Security group and some IAM roles to hook them all together. These are placed in the section of the serverless.yml. resources Define the AppSync GrpahQL API Let’s define the AWS AppSync resource, Add the following example config to the section of serverless.yml custom https://medium.com/media/765d21742279f0a537037d3b1ee293fd/href As you can see, each query and mutation has an entry in the mapping templates. Define the DynamoDB table The next section of this code example creates a DynamoDB table. PostsTable: Type: AWS::DynamoDB::Table Properties: TableName: ${self:custom.postsTable} AttributeDefinitions: - AttributeName: id AttributeType: S KeySchema: - AttributeName: id KeyType: HASH ProvisionedThroughput: ReadCapacityUnits: 5 WriteCapacityUnits: 1 StreamSpecification: StreamViewType: NEW_IMAGE This table has only a single hash key. The are kept low because DAX serves most of the read traffic. DynamoDB is called only if DAX has not cached the item. ProvisionedThroughput ReadCapacityUnits Define the DAX cluster Now let’s create DAX cluster, the template sets up following services: DAX cluster with one t2.small node. Security group with a rule to allow Lambda to send traffic to DAX on TCP port 8111. An IAM role allow DAX access to DynamoDB. A VPC refers to this security group. Security groups control how network traffic is allowed to flow in a VPC. https://medium.com/media/8d3a78df7bdef234caa4e5034f7a01b1/href Define VPC into Lambda To properly connect AWS Lambda to DAX, I need to deploy your lambda functions into the same VPC of DAX, Configure section in serverless.yml file: provider provider: vpc: securityGroupIds: - Fn::GetAtt: [DaxVpcSecurityGroup, GroupId] subnetIds: - Ref: daxSubnet1 - Ref: daxSubnet2 The other parts of the AWS configuration like authentication, schema, and data sources etc. you can find them in My . GitHub repo The code The lambda function code is in . The Lambda handler uses environment variables for configuration: is the name of the table containing post data, and is the DAX cluster endpoint. These variables are configured automatically in the serverless.yml. handler.js POSTS_TABLE_NAME DAX_ENDPOINT When there is mutation or query request, Appsync would invoke lambda function data source to insert or get data from DAX, If Lambda function raises an error, Pipeline resolver will go to next pipeline function and connect to DynamoDb datasource, get/put item from/to DynamoDb. https://medium.com/media/9a63674059e79e70365f2f6037a6beca/href Deploy your API To deploy your API, run the following: $ serverless deploy -v Conclusion In this post, I showed how to use Serverless framework to create Appsync lambda data source that uses DAX and DynamoDB to implement simple quey and mutation. I hope you have found this article useful, the full code example is available on my GitHub repo .