How to specify _HANDLER in AWS Lambda Docker Image

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I am trying to create a docker image to run a shell script as aws lambda function. As far as I understood, I need a runtime and a handler.

The default runtime (bootstrap) looks like this:

#!/bin/sh
set -euo pipefail

# Handler format: <script_name>.<bash_function_name>
#
# The script file <script_name>.sh  must be located at the root of your
# function's deployment package, alongside this bootstrap executable.
source $(dirname "$0")/"$(echo $_HANDLER | cut -d. -f1).sh"

while true
do
    # Request the next event from the Lambda runtime
    HEADERS="$(mktemp)"
    EVENT_DATA=$(curl -v -sS -LD "$HEADERS" -X GET "http://${AWS_LAMBDA_RUNTIME_API}/2018-06-01/runtime/invocation/next")
    INVOCATION_ID=$(grep -Fi Lambda-Runtime-Aws-Request-Id "$HEADERS" | tr -d '[:space:]' | cut -d: -f2)

    # Execute the handler function from the script
    RESPONSE=$($(echo "$_HANDLER" | cut -d. -f2) "$EVENT_DATA")

    # Send the response to Lambda runtime
    curl -v -sS -X POST "http://${AWS_LAMBDA_RUNTIME_API}/2018-06-01/runtime/invocation/$INVOCATION_ID/response" -d "$RESPONSE"
done

The Dockerfile:

FROM public.ecr.aws/lambda/provided:al2 

COPY bootstrap ${LAMBDA_RUNTIME_DIR}
COPY function.sh ${LAMBDA_TASK_ROOT}

RUN …  (install some dependencies)

CMD ["function.handler"]

From what I've read, your supposed to set CMD to the handler. However this does not seem to work as the $_HANDLER variable is not known inside of the container.

aws-lambda docker
1 Answers

I can't figure out what makes the difference, but this combination of Dockerfile and bootstrap works.

#!/bin/sh
set -euo pipefail

source "$LAMBDA_TASK_ROOT"/"$(echo $_HANDLER | cut -d. -f1).sh"

while true
do
    # Request the next event from the Lambda runtime
    HEADERS="$(mktemp)"
    EVENT_DATA=$(curl -sS -LD "$HEADERS" -X GET "http://${AWS_LAMBDA_RUNTIME_API}/2018-06-01/runtime/invocation/next")
    INVOCATION_ID=$(grep -Fi Lambda-Runtime-Aws-Request-Id "$HEADERS" | tr -d '[:space:]' | cut -d: -f2)

    # Execute the handler function from the script
    RESPONSE=$($(echo "$_HANDLER" | cut -d. -f2) "$EVENT_DATA")

    # Send the response to Lambda runtime
    curl -sS -X POST "http://${AWS_LAMBDA_RUNTIME_API}/2018-06-01/runtime/invocation/$INVOCATION_ID/response" -d "$RESPONSE"
done

FROM public.ecr.aws/lambda/provided:al2 

COPY ./bootstrap ${LAMBDA_RUNTIME_DIR}
COPY ./function.sh ${LAMBDA_TASK_ROOT}

RUN chmod 755 ${LAMBDA_RUNTIME_DIR}/bootstrap ${LAMBDA_TASK_ROOT}/function.sh

RUN … 

WORKDIR ${LAMBDA_TASK_ROOT} 
CMD ["function.handler"]
user_61989420
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