Lambda Testing scenario

The Lambda scenario is a variation on the classical architecture of the system-tests tailored to evaluate the AWS Lambda variants of the tracers when used to serve HTTP requests.

To achieve this we simulate the following AWS deployment architecture inside the system-tests using AWS provided tools :

graph LR
    A[Incoming HTTP Request] -->|HTTP| B[AWS Managed Load Balancer]
    B -->|event: request as JSON| C[AWS Lambda]

The AWS Managed Load Balancer could be any of the following ones:

• API Gateway
• Application Load Balancer
• Lambda function url service

To do this, we rely on two tools from AWS to emulate Lambda and Load Balancers:

• AWS Lambda Runtime Interface Emulator
• AWS SAM cli

Note: for now only the python variant (datadog_lambda) is being tested simulating an API Gateway

Key differences with end to end scenarios

To replace the AWS Managed Load Balancer, we run a dedicated container in front of the weblog named Lambda Proxy. It is responsible for converting the incoming request to a lambda event representation, invoking the lambda function running inside the weblog and converting back the return value of function to an http response.

The Lambda Function runs inside the Weblog Container thanks to the AWS Lambda Runtime Interface Emumlator.

There is no Agent Container, the Datadog Extension (equivalent to the Datadog Agent in the context of lambda) needs to run inside the Weblog Container, the Application Proxy Container therefore needs to send traces back to the Weblog Container.

flowchart TD
    TESTS[Tests Container] -->|Send Requests| LambdaProxy
    LambdaProxy[Lambda Proxy] -->|Send Lambda Event| Application
    subgraph APP[Application Container]
        socat[socat *:8127] --> Extension
        Extension[Extension localhost:8126]
        Application[Application *:8080]
    end
    Application --> | Send Traces | APPPROXY
    APPPROXY[Application Proxy] --> | Send back traces | socat
    APPPROXY -->|mitmdump| TESTS
    Extension --> AGENTPROXY
    AGENTPROXY[Agent Proxy] -->|remote request| BACKEND
    AGENTPROXY -->|mitmdump| TESTS
    BACKEND[Datadog] -->|trace API| TESTS

Specific considerations for the weblogs

On top of responding to the regular /healthcheck endpoint.

Lambda Weblogs should respond the same JSON dict response to the non HTTP event:

{
    "healthcheck": true
}

This is because the healthcheck is sent by the Lambda Weblog container itself which has no knowledge of how to serialize it as the event type expected by the weblog.