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Usage

Create a sample app with sam init command: sam init or sam init --runtime <favourite-runtime>

sam requires a SAM template in order to know how to invoke your function locally, and it’s also true for spawning API Gateway locally - If no template is specified template.yaml will be used instead.

Alternatively, you can find other sample SAM Templates by visiting SAM official repository.

Invoke functions locally

SAM CLI Invoke Sample

SAM CLI Invoke Sample

You can invoke your function locally by passing its --SAM logical ID-- and an event file. Alternatively, sam local invoke accepts stdin as an event too.

Resources:
  Ratings:  # <-- Logical ID
    Type: 'AWS::Serverless::Function'
  ...

Syntax

# Invoking function with event file
$ sam local invoke "Ratings" -e event.json

# Invoking function with event via stdin
$ echo '{"message": "Hey, are you there?" }' | sam local invoke "Ratings"

# For more options
$ sam local invoke --help

Run automated tests for your Lambda functions locally

You can use the sam local invoke command to manually test your code by running Lambda function locally. With SAM CLI, you can easily author automated integration tests by first running tests against local Lambda functions before deploying to the cloud. The sam local start-lambda command starts a local endpoint that emulates the AWS Lambda service’s invoke endpoint, and you can invoke it from your automated tests. Because this endpoint emulates the Lambda service's invoke endpoint, you can write tests once and run them (without any modifications) against the local Lambda function or against a deployed Lambda function. You can also run the same tests against a deployed SAM stack in your CI/CD pipeline.

Here is how this works:

1. Start the Local Lambda Endpoint

Start the local Lambda endpoint by running the following command in the directory that contains your AWS SAM template:

sam local start-lambda

This command starts a local endpoint at http://127.0.0.1:3001 that emulates the AWS Lambda service, and you can run your automated tests against this local Lambda endpoint. When you send an invoke to this endpoint using the AWS CLI or SDK, it will locally execute the Lambda function specified in the request and return a response.

2. Run integration test against local Lambda endpoint

In your integration test, you can use AWS SDK to invoke your Lambda function with test data, wait for response, and assert that the response what you expect. To run the integration test locally, you should configure AWS SDK to send Lambda Invoke API call to local Lambda endpoint started in previous step.

Here is an Python example (AWS SDK for other languages have similar configurations):

import boto3
import botocore

# Set "running_locally" flag if you are running the integration test locally
running_locally = True

if running_locally:

    # Create Lambda SDK client to connect to appropriate Lambda endpoint
    lambda_client = boto3.client('lambda',
        region_name="us-west-2",
        endpoint_url="http://127.0.0.1:3001",
        use_ssl=False,
        verify=False,
        config=botocore.client.Config(
            signature_version=botocore.UNSIGNED,
            read_timeout=0,
            retries={'max_attempts': 0},
        )
    )
else:
    lambda_client = boto3.client('lambda')


# Invoke your Lambda function as you normally usually do. The function will run
# locally if it is configured to do so
response = lambda_client.invoke(FunctionName="HelloWorldFunction")

# Verify the response
assert response == "Hello World"

This code can run without modifications against a Lambda function which is deployed. To do so, set the running_locally flag to False . This will setup AWS SDK to connect to AWS Lambda service on the cloud.

Connecting to docker network

Both sam local invoke and sam local start-api support connecting the create lambda docker containers to an existing docker network.

To connect the containers to an existing docker network, you can use the --docker-network command-line argument or the SAM_DOCKER_NETWORK environment variable along with the name or id of the docker network you wish to connect to.

# Invoke a function locally and connect to a docker network
$ sam local invoke --docker-network my-custom-network <function logical id>

# Start local API Gateway and connect all containers to a docker network
$ sam local start-api --docker-network b91847306671 -d 5858

Generate sample event payloads

To make local development and testing of Lambda functions easier, you can generate and customize event payloads for the following services:

  • Amazon Alexa
  • Amazon API Gateway
  • AWS Batch
  • AWS CloudFormation
  • Amazon CloudFront
  • AWS CodeCommit
  • AWS CodePipeline
  • Amazon Cognito
  • AWS Config
  • Amazon DynamoDB
  • Amazon Kinesis
  • Amazon Lex
  • Amazon Rekognition
  • Amazon S3
  • Amazon SES
  • Amazon SNS
  • Amazon SQS
  • AWS Step Functions

Syntax

$ sam local generate-event <service> <event>

You can generate multiple types of events from each service. For example, to generate the event from S3 when a new object is created, use:

$ sam local generate-event s3 put

To generate the event from S3 when an object is deleted, you can use:

$ sam local generate-event s3 delete

For more options, see sam local generate-event --help.

Run API Gateway locally

sam local start-api spawns a local API Gateway to test HTTP request/response functionality. Features hot-reloading to allow you to quickly develop and iterate over your functions.

SAM CLI Start API

SAM CLI Start API

Syntax

$ sam local start-api

sam will automatically find any functions within your SAM template that have Api event sources defined, and mount them at the defined HTTP paths.

In the example below, the Ratings function would mount ratings.py:handler() at /ratings for GET requests.

Ratings:
  Type: AWS::Serverless::Function
  Properties:
    Handler: ratings.handler
    Runtime: python3.6
    Events:
      Api:
        Type: Api
        Properties:
          Path: /ratings
          Method: get

By default, SAM uses Proxy Integration and expects the response from your Lambda function to include one or more of the following: statusCode, headers and/or body.

For example:

// Example of a Proxy Integration response
exports.handler = (event, context, callback) => {
    callback(null, {
        statusCode: 200,
        headers: { "x-custom-header" : "my custom header value" },
        body: "hello world"
    });
}

For examples in other AWS Lambda languages, see this page.

If your function does not return a valid Proxy Integration response then you will get a HTTP 500 (Internal Server Error) when accessing your function. SAM CLI will also print the following error log message to help you diagnose the problem:

ERROR: Function ExampleFunction returned an invalid response (must include one of: body, headers or statusCode in the response object)

Debugging Applications

Both sam local invoke and sam local start-api support local debugging of your functions.

To run SAM Local with debugging support enabled, just specify --debug-port or -d on the command line.

# Invoke a function locally in debug mode on port 5858
$ sam local invoke -d 5858 <function logical id>

# Start local API Gateway in debug mode on port 5858
$ sam local start-api -d 5858

Note: If using sam local start-api, the local API Gateway will expose all of your Lambda functions but, since you can specify a single debug port, you can only debug one function at a time. You will need to hit your API before SAM CLI binds to the port allowing the debugger to connect.

Here is an example showing how to debug a NodeJS function with Microsoft Visual Studio Code:

SAM Local debugging example

SAM Local debugging example

In order to setup Visual Studio Code for debugging with AWS SAM CLI, use the following launch configuration:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Attach to SAM CLI",
            "type": "node",
            "request": "attach",
            "address": "localhost",
            "port": 5858,
            "localRoot": "${workspaceRoot}",
            "remoteRoot": "/var/task",
            "protocol": "legacy"
        }
    ]
}

Note: Node.js versions --below-- 7 (e.g. Node.js 4.3 and Node.js 6.10) use the legacy protocol, while Node.js versions including and above 7 (e.g. Node.js 8.10) use the inspector protocol. Be sure to specify the corresponding protocol in the protocol entry of your launch configuration.

Debugging Python functions

Unlike Node.JS and Java, Python requires you to enable remote debugging in your Lambda function code. If you enable debugging with --debug-port or -d for a function that uses one of the Python runtimes, SAM CLI will just map through that port from your host machine through to the Lambda runtime container. You will need to enable remote debugging in your function code. To do this, use a python package such as remote-pdb. When configuring the host the debugger listens on in your code, make sure to use 0.0.0.0 not 127.0.0.1 to allow Docker to map through the port to your host machine.

Please note, due to a open bug with Visual Studio Code, you may get a Debug adapter process has terminated unexpectedly error when attempting to debug Python applications with this IDE. Please track the GitHub issue for updates.

Debugging Golang functions

Golang function debugging is slightly different when compared to Node.JS, Java, and Python. We require delve as the debugger, and wrap your function with it at runtime. The debugger is run in headless mode, listening on the debug port.

When debugging, you must compile your function in debug mode:

`GOARCH=amd64 GOOS=linux go build -gcflags='-N -l' -o <output path> <path to code directory>

You must compile delve to run in the container and provide its local path via the --debugger-path argument. Build delve locally as follows:

GOARCH=amd64 GOOS=linux go build -o <delve folder path>/dlv github.com/derekparker/delve/cmd/dlv

NOTE: The output path needs to end in /dlv. The docker container will expect the dlv binary to be in the <delve folder path> and will cause mounting issue otherwise.

Then invoke sam similar to the following:

sam local start-api -d 5986 --debugger-path <delve folder path>

NOTE: The --debugger-path is the path to the directory that contains the dlv binary compiled from the above.

The following is an example launch configuration for Visual Studio Code to attach to a debug session.

{
  "version": "0.2.0",
  "configurations": [
  {
      "name": "Connect to Lambda container",
      "type": "go",
      "request": "launch",
      "mode": "remote",
      "remotePath": "",
      "port": <debug port>,
      "host": "127.0.0.1",
      "program": "${workspaceRoot}",
      "env": {},
      "args": [],
    },
  ]
}

Passing Additional Runtime Debug Arguments

To pass additional runtime arguments when debugging your function, use the environment variable DEBUGGER_ARGS. This will pass a string of arguments directly into the run command SAM CLI uses to start your function.

For example, if you want to load a debugger like iKPdb at runtime of your Python function, you could pass the following as DEBUGGER_ARGS: -m ikpdb --ikpdb-port=5858 --ikpdb-working-directory=/var/task/ --ikpdb-client-working-directory=/myApp --ikpdb-address=0.0.0.0. This would load iKPdb at runtime with the other arguments you’ve specified. In this case, your full SAM CLI command would be:

$ DEBUGGER_ARGS="-m ikpdb --ikpdb-port=5858 --ikpdb-working-directory=/var/task/ --ikpdb-client-working-directory=/myApp --ikpdb-address=0.0.0.0" echo {} | sam local invoke -d 5858 myFunction

You may pass debugger arguments to functions of all runtimes.

To simplify troubleshooting, we added a new command called sam logs to SAM CLI. sam logs lets you fetch logs generated by your Lambda function from the command line. In addition to printing the logs on the terminal, this command has several nifty features to help you quickly find the bug. Note: This command works for all AWS Lambda functions; not just the ones you deploy using SAM.

Fetch, tail, and filter Lambda function logs

To simplify troubleshooting, SAM CLI has a command called sam logs. sam logs lets you fetch logs generated by your Lambda function from the command line. In addition to printing the logs on the terminal, this command has several nifty features to help you quickly find the bug.

Note: This command works for all AWS Lambda functions; not just the ones you deploy using SAM.

Basic Usage: Using CloudFormation Stack

When your function is a part of a CloudFormation stack, you can fetch logs using the function's LogicalID:

sam logs -n HelloWorldFunction --stack-name mystack

Basic Usage: Using Lambda Function name

Or, you can fetch logs using the function's name

sam logs -n mystack-HelloWorldFunction-1FJ8PD

Tail Logs

Add --tail option to wait for new logs and see them as they arrive. This is very handy during deployment or when troubleshooting a production issue.

sam logs -n HelloWorldFunction --stack-name mystack --tail

View logs for specific time range You can view logs for specific time range using the -s and -e options

sam logs -n HelloWorldFunction --stack-name mystack -s '10min ago' -e '2min ago'

Filter Logs

Use the --filter option to quickly find logs that match terms, phrases or values in your log events

sam logs -n HelloWorldFunction --stack-name mystack --filter "error"

In the output, SAM CLI will underline all occurrences of the word “error” so you can easily locate the filter keyword within the log output.

Error Highlighting

When your Lambda function crashes or times out, SAM CLI will highlight the timeout message in red. This will help you easily locate specific executions that are timing out within a giant stream of log output.

SAM CLI Logs Error Highlighting

JSON pretty printing

If your log messages print JSON strings, SAM CLI will automatically pretty print the JSON to help you visually parse and understand the JSON.

SAM CLI Logs JSON Pretty Print

Validate SAM templates

Validate your templates with $ sam validate. Currently this command will validate that the template provided is valid JSON / YAML. As with most SAM CLI commands, it will look for a template.[yaml|yml] file in your current working directory by default. You can specify a different template file/location with the -t or --template option.

Syntax

$ sam validate
<path-to-file>/template.yml is a valid SAM Template

Note: The validate command requires AWS credentials to be configured. See IAM Credentials.

Package and Deploy to Lambda

Once you have developed and tested your Serverless application locally, you can deploy to Lambda using sam package and sam deploy command.

sam package command will zip your code artifacts, upload to S3 and produce a SAM file that is ready to be deployed to Lambda using AWS CloudFormation.

sam deploy command will deploy the packaged SAM template to CloudFormation.

Both sam package and sam deploy are identical to their AWS CLI equivalents commands aws cloudformation package and aws cloudformation deploy respectively - Please consult the AWS CLI command documentation for usage.

Example:

# Package SAM template
$ sam package --template-file sam.yaml --s3-bucket mybucket --output-template-file packaged.yaml

# Deploy packaged SAM template
$ sam deploy --template-file ./packaged.yaml --stack-name mystack --capabilities CAPABILITY_IAM

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