\nAWS Lambda is a\u00a0serverless compute\u00a0service that runs our code in response to events and automatically manages the underlying compute resources for us. We can use AWS Lambda to extend other AWS services with custom logic, or create our own back-end services that operate at AWS scale, performance, and security. AWS Lambda can automatically run code in response to\u00a0multiple events, such as HTTP requests via\u00a0Amazon API Gateway, modifications to objects in\u00a0Amazon S3\u00a0buckets, table updates in\u00a0Amazon DynamoDB, and state transitions in\u00a0AWS Step Functions.<\/p>\n
Lambda runs our code on high-availability compute infrastructure and performs all the administration of the compute resources, including server and operating system maintenance, capacity provisioning and automatic scaling, code and security patch deployment, and code monitoring and logging. All we need to do is supply the code.<\/p>\n
Now, lets\u2019 start with building an API that will help a local movie rental shop in managing their available movies.<\/p>\n
API architecture<\/h2>\n
The following diagram shows how the API Gateway and Lambda fit into the API architecture:<\/p>\n
AWS Lambda empowers microservice development. That being said, each endpoint triggers a different Lambda function. These functions are independent of one another and can be written in different languages, thereby leading to scaling at function level, easier unit testing, and loose coupling.<\/p>\n All requests from clients first go\u00a0through\u00a0the API Gateway. It then routes the incoming request to the right Lambda function accordingly.<\/p>\n Note that a single Lambda function can Handle multiple HTTP methods (GET<\/strong>, POST<\/strong>, PUT<\/strong>, DELETE<\/strong>, and so on). It\u2019s advisable to create multiple Lambda functions for each functionality in order to leverage the power of microservices. However, building a single Lambda function to handle multiple endpoints could be a good exercise.<\/p>\n Now that the\u00a0architecture\u00a0has been defined, it\u2019s time to go through the implementation of the functionalities described in the above diagram.\u00a0Instead of hard coding the HTTP status code, you can use the net\/http<\/strong> Go package and use a built-in status code variables such as http.StatusOK<\/strong>, http.StatusCreated<\/strong>, http.StatusBadRequest<\/strong>, http.StatusInternalServerError<\/strong>, and so on.<\/p>\n The first feature to\u00a0implement\u00a0is listing movies. That\u2019s where the\u00a0GET\u00a0<\/strong>method comes into play. Lets\u2019 start with it following steps:<\/p>\n Step 1:<\/strong> Create a Lambda function that registers a\u00a0findAll\u00a0<\/strong>handler. This handler transforms a list of\u00a0movies to a\u00a0string and then returns this string wrapped by the\u00a0APIGatewayProxyResponse\u00a0<\/strong>variable along with a 200<\/strong> HTTP status code. It also handles errors in case of conversion failure. The handler implementation is as follows:<\/p>\n Instead of hard coding the HTTP status code, you can use the net\/http<\/strong> Go package and use a built-in status code variables such as http.StatusOK<\/strong>, http.StatusCreated<\/strong>, http.StatusBadRequest<\/strong>, http.StatusInternalServerError<\/strong>, and so on.<\/p>\n Step 2:<\/strong> Create a script file with the following content to build a Lambda function deployment package, a .zip<\/strong> file consisting of your code and any dependencies, as follows:<\/p>\n Step 3:<\/strong>\u00a0Execute the following commands to build the deployment package as .zip<\/strong> file:<\/p>\n Step 4:<\/strong> Configure AWS CLI using steps mentioned here<\/a>. Once configured, create an AWS role with name as\u00a0FindAllMoviesRole<\/strong> following the steps mentioned here<\/a>\u00a0and verify if it is successfully created:<\/p>\n Above command should give the response as shown in a screenshot below:<\/p>\n Step 5:<\/strong> Next, create a new Lambda function using the AWS CLI as follows:<\/p>\n Once function is created it will give us the output same as shown in a screenshot below:<\/p>\n Step 6<\/strong>: Heading back to the AWS Lambda Console, you should see that the function has been created successfully:<\/p>\n Step 7<\/strong>: Create a\u00a0sample\u00a0event with an empty JSON, as the function doesn\u2019t expect any argument, and click on the\u00a0Test<\/strong>\u00a0button:<\/p>\n You will notice in the previous screenshot that the function returns the expected output in a JSON format.<\/p>\n Step 8:<\/strong> Now that the function has been defined, you need to create a new API Gateway in order to trigger it:<\/p>\n Step 9:<\/strong> Next, from\u00a0the Actions<\/strong>\u00a0drop-down list, select\u00a0Create resource<\/strong>\u00a0and name it\u00a0movies<\/strong>:<\/p>\n Step 10:<\/strong> Expose a GET<\/strong> method on this\u00a0\/movies<\/strong>\u00a0resource by clicking on\u00a0Create Method<\/strong>. Choose\u00a0Lambda Function<\/strong>\u00a0under the\u00a0Integration type<\/strong>\u00a0section and select the\u00a0FindAllMovies<\/strong>\u00a0function:<\/p>\n Step 11:<\/strong> To deploy the API, select\u00a0Deploy API<\/strong>\u00a0from the\u00a0Actions<\/strong>\u00a0drop-down list.\u00a0You\u2019ll be prompted to create a new deployment stage:<\/p>\n Step 12:<\/strong> Once the deployment stage is created, an invocation URL will be displayed:<\/p>\n Step 13:<\/strong> Point your browser to the URL given or use a modern REST client like Postman or Insomnia. You can go with the cURL<\/strong> tool as it is installed by default on almost all operating systems:<\/p>\n The above command will return a list of movies in a JSON format:<\/p>\n When\u00a0calling\u00a0the\u00a0GET\u00a0<\/strong>endpoint, the request will go through the API Gateway, which will trigger the\u00a0findAll<\/strong> handler. This returns a response proxied by the API Gateway to the client in a JSON format.<\/p>\n Now that the\u00a0findAll\u00a0<\/strong>function has been deployed, you can implement a\u00a0findOne\u00a0<\/strong>function to search for a movie by its ID.<\/p>\n The\u00a0findOne<\/strong> handler\u00a0expects the APIGatewayProxyRequest <\/strong>argument that contains the event input. Then, it uses the\u00a0PathParameters\u00a0<\/strong>method to get the movie ID and validate it.<\/p>\n If the ID provided is not a valid number, the\u00a0Atoi\u00a0<\/strong>method will return an error, and a 500<\/strong> error code will be returned to the client. Otherwise, a movie will be fetched based on the index and returned to the client with a 200 OK<\/strong> status wrapped in\u00a0APIGatewayProxyResponse<\/strong>:<\/p>\n Similar to the\u00a0FindAllMovies\u00a0<\/strong>function, create a new Lambda function for searching for a movie:<\/p>\n Go back to API Gateway console, create a new resource, expose the GET\u00a0<\/strong>method, and then link the resource to the FindOneMovie\u00a0<\/strong>function.\u00a0Note the use of the\u00a0{id}<\/strong>\u00a0placeholder in the path. The value of\u00a0id\u00a0will be made available via the\u00a0APIGatewayProxyResponse\u00a0<\/strong>object. The following screenshot depicts this:<\/p>\n Redeploy the API and\u00a0use\u00a0the following cURL<\/strong> command to test the endpoint:<\/p>\n The following JSON will be returned:<\/p>\n When the API URL is invoked with an ID, the movie corresponding to the ID is returned if it exists.<\/p>\n Now you know how the GET<\/strong> method\u00a0works with and without path parameters. The next step is to pass a JSON payload to a Lambda function through the API Gateway. The code is self-explanatory. It converts the request input to a movie structure, adds it to the list of movies, and returns the new list of movies in a JSON format:<\/p>\n Next, create a new Lambda function for\u00a0InsertMovie<\/strong> with the following command:<\/p>\n Next, create a\u00a0POST\u00a0<\/strong>method on the\u00a0\/movies<\/strong>\u00a0resource and link it to the InsertMovie<\/strong> function:<\/p>\n To test it out, use the following cURL<\/strong> command with the\u00a0POST\u00a0<\/strong>verb and the\u00a0-d<\/strong>\u00a0flag, followed by a JSON string (with the\u00a0id\u00a0and\u00a0name\u00a0attributes):<\/p>\n The above command will return the following JSON response:<\/p>\n As you can see, the new movie has been inserted successfully. If you test it again, it should work as expected:<\/p>\n The preceding command will return the following JSON response:<\/p>\n As you can see, it was\u00a0successful\u00a0and the movie was again inserted as expected, but what if you wait few minutes and try to insert a third movie? The following command will be used to execute it again:<\/p>\n Once again, a new JSON response will be returned:<\/p>\n You will find that the movies with IDs 6 and 7 have been removed; why did this happen?\u00a0 It\u2019s simple. Lambda functions are stateless.<\/p>\n When the\u00a0InsertMovie <\/strong>function is invoked for the first time (first insert), AWS Lambda creates a container and deploys the function payload to the container. Then, it remains active for a few minutes before it is terminated (warm start<\/strong>), which explains why the second\u00a0insert passed. In the third insert, the container is already terminated, and hence Lambda creates a new container (cold start<\/strong>) to handle the insert.<\/p>\n This is why the previous state is lost. The following diagram illustrates the cold\/warm start issue:<\/p>\n This explains why Lambda\u00a0functions\u00a0should be stateless and why you should not make any assumptions that the state will be preserved from one invocation to the next.<\/p>\n Complete source code is hosted on\u00a0github<\/a>.<\/p>\n![\"RESTful](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/11\/image1.png\")
<\/a><\/p>\nEndpoints design<\/h2>\n
The GET method<\/h2>\n
package main\r\n\r\nimport (\r\n \"encoding\/json\"\r\n\r\n \"github.com\/aws\/aws-lambda-go\/events\"\r\n \"github.com\/aws\/aws-lambda-go\/lambda\"\r\n)\r\n\r\nvar movies = []struct {\r\n ID int `json:\"id\"`\r\n Name string `json:\"name\"`\r\n}{\r\n {\r\n ID: 1,\r\n Name: \"Avengers\",\r\n },\r\n {\r\n ID: 2,\r\n Name: \"Ant-Man\",\r\n },\r\n {\r\n ID: 3,\r\n Name: \"Thor\",\r\n },\r\n {\r\n ID: 4,\r\n Name: \"Hulk\",\r\n }, {\r\n ID: 5,\r\n Name: \"Doctor Strange\",\r\n },\r\n}\r\n\r\nfunc findAll() (events.APIGatewayProxyResponse, error) {\r\n response, err := json.Marshal(movies)\r\n if err != nil {\r\n return events.APIGatewayProxyResponse{}, err\r\n }\r\n\r\n return events.APIGatewayProxyResponse{\r\n StatusCode: 200,\r\n Headers: map[string]string{\r\n \"Content-Type\": \"application\/json\",\r\n },\r\n Body: string(response),\r\n }, nil\r\n}\r\n\r\nfunc main() {\r\n lambda.Start(findAll)\r\n}<\/pre>\n#!\/bin\/bash\r\n\r\necho \"Build the binary\"\r\nGOOS=linux GOARCH=amd64 go build -o main main.go\r\n\r\necho \"Create a ZIP file\"\r\nzip deployment.zip main\r\n\r\necho \"Cleaning up\"\r\nrm main<\/pre>\n
$ chmod +x build.sh\r\n$ .\/build.sh<\/pre>\n
$ aws iam get-role --role-name FindAllMoviesRole<\/pre>\n
<\/a>aws lambda create-function --function-name FindAllMovies \\\r\n --zip-file fileb:\/\/deployment.zip \\\r\n --runtime go1.x --handler main \\\r\n --role arn:aws:iam::ACCOUNT_ID:role\/FindAllMoviesRole \\\r\n --region us-east-1<\/pre>\n
<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\ncurl -sX GET https:\/\/51cxzthvma.execute-api.us-east-1.amazonaws.com\/staging\/movies | jq '.'<\/pre>\n
<\/a><\/p>\nThe GET method with parameters<\/h2>\n
...\r\n\r\nfunc findOne(req events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {\r\n\r\n\u00a0 id, err := strconv.Atoi(req.PathParameters[\"id\"])\r\n\r\n\u00a0 if err != nil {\r\n\r\n\u00a0\u00a0\u00a0 return events.APIGatewayProxyResponse{\r\n\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 StatusCode: 500,\r\n\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 Body:\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \"ID must be a number\",\r\n\r\n\u00a0\u00a0\u00a0 }, nil\r\n\r\n\u00a0 }\r\n\r\n\u00a0 response, err := json.Marshal(movies[id-1])\r\n\r\n\u00a0 if err != nil {\r\n\r\n\u00a0\u00a0\u00a0 return events.APIGatewayProxyResponse{\r\n\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 StatusCode: 500,\r\n\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 Body:\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 err.Error(),\r\n\r\n\u00a0\u00a0\u00a0 }, nil\r\n\r\n\u00a0 }\r\n\r\n\u00a0 return events.APIGatewayProxyResponse{\r\n\r\n\u00a0\u00a0\u00a0 StatusCode: 200,\r\n\r\n\u00a0\u00a0\u00a0 Headers: map[string]string{\r\n\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 \"Content-Type\": \"application\/json\",\r\n\r\n\u00a0\u00a0\u00a0 },\r\n\r\n\u00a0\u00a0\u00a0 Body: string(response),\r\n\r\n\u00a0 }, nil\r\n\r\n}\r\n\r\nfunc main() {\r\n\r\n\u00a0 lambda.Start(findOne)\r\n\r\n}<\/pre>\naws lambda create-function --function-name FindOneMovie \\\r\n --zip-file fileb:\/\/deployment.zip \\\r\n --runtime go1.x --handler main \\\r\n --role arn:aws:iam::ACCOUNT_ID:role\/FindOneMovieRole \\\r\n --region us-east-1<\/pre>\n
<\/a><\/p>\ncurl -sX https:\/\/51cxzthvma.execute-api.us-east-1.amazonaws.com\/staging\/movies\/1 | jq '.'<\/pre>\n
<\/a><\/p>\nThe POST method<\/h2>\n
package main\r\n\r\nimport (\r\n \"encoding\/json\"\r\n \"strconv\"\r\n \"github.com\/aws\/aws-lambda-go\/events\"\r\n \"github.com\/aws\/aws-lambda-go\/lambda\"\r\n)\r\n\r\ntype Movie struct {\r\n ID int `json:\"id\"`\r\n Name string `json:\"name\"`\r\n}\r\n\r\nvar movies = []Movie{\r\n Movie{\r\n ID: 1,\r\n Name: \"Avengers\",\r\n },\r\n ...\r\n}\r\n\r\nfunc insert(req events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {\r\n var movie Movie\r\n err := json.Unmarshal([]byte(req.Body), &movie)\r\n if err != nil {\r\n return events.APIGatewayProxyResponse{\r\n StatusCode: 400,\r\n Body: \"Invalid payload\",\r\n }, nil\r\n }\r\n\r\n movies = append(movies, movie)\r\n\r\n response, err := json.Marshal(movies)\r\n if err != nil {\r\n return events.APIGatewayProxyResponse{\r\n StatusCode: 500,\r\n Body: err.Error(),\r\n }, nil\r\n }\r\n\r\n return events.APIGatewayProxyResponse{\r\n StatusCode: 200,\r\n Headers: map[string]string{\r\n \"Content-Type\": \"application\/json\",\r\n },\r\n Body: string(response),\r\n }, nil\r\n}\r\n\r\nfunc main() {\r\n lambda.Start(insert)\r\n}<\/pre>\naws lambda create-function --function-name InsertMovie \\\r\n --zip-file fileb:\/\/deployment.zip \\\r\n --runtime go1.x --handler main \\\r\n --role arn:aws:iam::ACCOUNT_ID:role\/InsertMovieRole \\\r\n --region us-east-1<\/pre>\n
<\/a><\/p>\ncurl -sX POST -d '{\"id\":6, \"name\": \"Spiderman:Homecoming\"}' https:\/\/51cxzthvma.execute-api.us-east-1.amazonaws.com\/staging\/movies | jq '.'<\/pre>\n<\/a><\/p>\ncurl -sX POST -d '{\"id\":7, \"name\": \"Iron man\"}' https:\/\/51cxzthvma.execute-api.us-east-1.amazonaws.com\/staging\/movies | jq '.'<\/pre>\n<\/a><\/p>\ncurl -sX POST -d '{\"id\":8, \"name\": \"Captain America\"}' https:\/\/51cxzthvma.execute-api.us-east-1.amazonaws.com\/staging\/movies | jq '.'<\/pre>\n<\/a><\/p>\n<\/a><\/p>\n