A short script to retrieve logs from a specified Lambda function in a specified CloudFormation stack.

view-function-log.sh

#!/bin/bash

# A script to view logs for a specific Lambda function in a CloudFormation stack.

set -e
set -o pipefail

function usage() {
  echo "View logs for a specific Lambda function in a CloudFormation stack."
  echo "Usage: $0 -s <stack-name> -f <function-name> [-r <region>] [<other-aws-logs-args>]"
  echo ""
  echo "  -s, --stack-name       The name of the CloudFormation stack."
  echo "  -f, --function-name    The name of the Lambda function (as defined in the stack)."
  echo "  -r, --region           AWS region (default: eu-west-1)."
  echo
  echo "  (all other arguments)  Additional arguments to pass to 'aws logs tail'."
}

# Check for jq
if ! command -v jq &> /dev/null; then
  echo "'jq' is required to review and select the most recent log group."
  echo "Please install 'jq' to use this script (eg. `brew install jq` on macOS)."
  exit 1
fi

# Defaults
STACK_NAME=""
FUNCTION_NAME=""
OTHER_ARGS=()
REGION="eu-west-1"

while [[ $# -gt 0 ]]; do
  case $1 in
    -s|--stack-name)
      STACK_NAME="$2"
      shift 2
      ;;
    -f|--function-name)
      FUNCTION_NAME="$2"
      shift 2
      ;;
    -r | --region)
      REGION="$2"
      shift 2
      ;;
    -h|--help)
      usage
      exit 0
      ;;
    *)
      OTHER_ARGS+=("$1")
      shift
      ;;
  esac
done

# Validate inputs - stack and function name are required
if [ -z "$STACK_NAME" ] || [ -z "$FUNCTION_NAME" ]; then
  usage
  exit 1
fi

# Find the log group
LOG_GROUP_PREFIX="/aws/lambda/${STACK_NAME}"


# Use AWS CLI to find the log group name by listing all and grepping
# Sort by creationTime to get the most recent log group if multiple exist
# echo "Searching for log group with prefix '$LOG_GROUP_PREFIX' containing '$FUNCTION_NAME'..."
LOG_GROUP_NAME=$(aws logs describe-log-groups \
  --region "$REGION" \
  --log-group-name-prefix "$LOG_GROUP_PREFIX" \
  --query "logGroups[?contains(logGroupName, '$FUNCTION_NAME')].[creationTime, logGroupName]" \
  --output json | jq -r 'sort_by(.[0]) | reverse | .[0][1]')

# Check if a log group was found
if [ -z "$LOG_GROUP_NAME" ] || [ "$LOG_GROUP_NAME" == "null" ]; then
  echo "No log group found for stack '$STACK_NAME' and function '$FUNCTION_NAME'."
  exit 1
fi

# echo "Using most recent log group: $LOG_GROUP_NAME"
# echo "Additional arguments: ${OTHER_ARGS[*]}"
exec aws logs tail "$LOG_GROUP_NAME" --region "$REGION" "${OTHER_ARGS[@]}"

Typical usage

./view-function-log.sh -s <stack> -f <function> -r <region> --since 10m