AWS Lambda: Invoke a Function from CLI

Invoking Lambda Functions from the CLI

The aws lambda invoke command triggers a Lambda function and captures its response. It supports synchronous and asynchronous invocation, payload input, and execution log tailing.

Basic Synchronous Invocation

aws lambda invoke \
  --function-name my-processor \
  --payload '{"action": "process", "id": 42}' \
  response.json

The response payload is written to response.json. The command itself returns metadata like status code and executed version.

Invocation Types

Type	Flag Value	Behavior
Synchronous	RequestResponse (default)	Waits for function to complete, returns response
Asynchronous	Event	Queues the invocation, returns immediately (status 202)
Dry Run	DryRun	Validates permissions without executing (status 204)

Async Invocation

aws lambda invoke \
  --function-name my-processor \
  --invocation-type Event \
  --payload '{"action": "batch-process"}' \
  /dev/null

Invoke with Log Tailing

aws lambda invoke \
  --function-name my-function \
  --payload '{"key": "value"}' \
  --log-type Tail \
  --query 'LogResult' \
  --output text response.json | base64 --decode

The --log-type Tail flag returns the last 4KB of execution logs, base64-encoded. Piping through base64 --decode reveals the actual log output.

Invoke a Specific Version or Alias

aws lambda invoke \
  --function-name my-function \
  --qualifier prod \
  response.json

Payload from File

aws lambda invoke \
  --function-name my-function \
  --payload file://event.json \
  response.json

Using file:// reads the payload from a local file, which is cleaner for complex JSON inputs.