Autosave: 2023-04-10 19:36:55

DevOps/AWS/AWS_Api_Gateway.md

@@ -0,0 +1,14 @@
+---
+categories:
+  - DevOps
+  - Backend
+tags: [AWS, aws-api-api-gateway, APIs]
+---
+
+# AWS API Gateway
+
+We can use Gateway as the front-door to our application. It will create an [HTTP](/Databases/REST/HTTP_request_types.md) endpoint that you can call from a client. In response to a client request you can then call a [lambda function](/DevOps/AWS/AWS_Lambda/Lambda_handler_function.md) that executes a backend process.
+
+![](/_img/gateway-services.png)
+
+See [using API Gateway as Lambda trigger](/DevOps/AWS/AWS_Lambda/Practical_walkthrough_Lambda_creation.md) for a basic example of usage.

DevOps/AWS/AWS_Lambda/Lambda_examples.md

@@ -26,3 +26,11 @@ exports.handler = (event, context, callback) => {
   return callback(null, request);
 };
 ```
+
+Let's walk through the above example making reference to the general structure of the [AWS Lambda handler function](/DevOps/AWS/AWS_Lambda/Lambda_handler_function.md):
+
+1. The `event` parameter is invoked to gain access to the event that triggered the function. This is a CloudFront request event which is targetted with `event.Records[0].cf.request`
+2. We classify this request as the `olduri` since it doesn't have the form we want.
+3. We mutate the original request by replacing `/` with `/index.html`
+4. We then re-assign the `request.uri` value to the value of the new URI.
+5. Finally we invoke the `callback` parameter to signal the completion of the transformation and return the new request as the return value.

DevOps/AWS/AWS_Lambda/Lambda_triggers.md

@@ -2,7 +2,7 @@
 categories:
   - DevOps
   - Backend
-tags: [AWS, aws-lambda, node-js, python]
+tags: [AWS, aws-lambda]
 ---
 
 # AWS Lambda triggers

DevOps/AWS/AWS_Lambda/Practical_walkthrough_Lambda_creation.md

@@ -0,0 +1,70 @@
+---
+categories:
+  - DevOps
+  - Backend
+tags: [AWS, aws-lambda, node-js]
+---
+
+# Practical walkthrough of creating a Lambda function, trigger and subsequent events
+
+## Basic set-up
+
+First we name the function and accept the defaults:
+
+![](/_img/lambda_func_one.png)
+
+This presents us with the function dashboard - a graphical representation of the Lambda showing [triggers]() as an input and destination as an output:
+
+![](/_img/lambda-func-two.png)
+
+Beneath this we have a code editor with the handler function with a basic boilerplate:
+
+![](/_img/lambda-func-three.png)
+
+## Adding a trigger
+
+Next we need to add a trigger that execute the handler.
+
+We will do this using [AWS API Gateway](/DevOps/AWS/AWS_Api_Gateway.md). We select "Add trigger" from the dashboard view and input basic settings:
+
+![](/_img/api-gateway-trigger.png)
+
+Now we see this step displayed in the dashboard:
+
+![](/_img/lambda-overview.png)
+
+With the endpoint and other settings displayed:
+
+![](/_img/trigger-info.png)
+
+If we go to the endpoint URL (`https://4kjqwbvd7g.execute-api.us-east-1.amazonaws.com/default/myFirstFunction`), we will see the output: `Hello from Lambda`.
+
+## Handling parameters
+
+We can make the example more realistic by expanding the handler to accept query parameters. We do this by accessing the value `queryStringParameters` on the `event` object:
+
+```js
+exports.handler = async (event) => {
+  const name = event.queryStringParameters && event.queryStringParameters.name;
+
+  let message = "Hello Lambda";
+
+  if (name !== null) {
+    message = `Hello ${name}`;
+  }
+
+  const response {
+    statusCode: 200,
+    body: JSON.stringify(message)
+
+  }
+};
+```
+
+If we now access `https://4kjqwbvd7g.execute-api.us-east-1.amazonaws.com/default/myFirstFunction?name=Thomas`
+
+We get `Hello Thomas` as output.
+
+For a more advanced API with multiple endpoints and parameters, it's easiest to use Postman:
+
+![](/_img/postman-lambda.png)