An AWS Lambda runtime in bash

README.txt

Invoke with SQS.

{ command: "ls $1", "argv": "/tmp" }

runtime.sh

#!/bin/bash
# TODO: add a trap in the process_payload function to fail outright and prevent
# unnecessary retries
set -eu

BUCKET=${XARGS_LAMBDA_BUCKET_NAME:-""}
PREFIX=${XARGS_LAMBDA_BUCKET_PREFIX:-"b"}

if [ -z "$BUCKET" ]; then
  echo 'missing required configuration XARGS_LAMBDA_BUCKET_NAME in env'
  exit 2
fi

# Parse the payload out of an SQS event.
# Looks like { command: string, output_queue: string, argv: string }
get_event_payloads() {
  echo $1 | jq '.Records[].body | fromjson'
}

# Run the script and send the output to the runtime API
process_payload() {
  REQUEST_ID=$1
  DATA_FILE=$2
  CMD_FILE=$(mktemp)

  jq -cr .command < "$DATA_FILE" > "$CMD_FILE"
  QUEUE=$(jq -cr .output_queue < "$DATA_FILE")
  ARGV=$(jq -cr .argv < "$DATA_FILE")

  echo "running $(<$CMD_FILE) $ARGV"

  # run the command and collect the output
  STDOUT=$(mktemp)
  STDERR=$(mktemp)
  # tee to files while keeping stdin and stderr as separate streams
  # bash $CMD_FILE $ARGV > >(tee -a $STDOUT) 2> >(tee -a $STDERR >&2)
  # never mind, /dev/fd doesn't exist in lambda, and you're not root so no ln hax
  # whatever it doesn't really matter
  bash $CMD_FILE $ARGV 2>"$STDERR" >"$STDOUT"
  cat $STDOUT $STDERR

  DATA="{\"stdout\": \"$(base64 -w 0 < $STDOUT)\", \"stderr\": \"$(base64 -w 0 < $STDERR)\"}"

  # send the response to the runtime api
  curl -s -X POST \
    "http://${AWS_LAMBDA_RUNTIME_API}/2018-06-01/runtime/invocation/$REQUEST_ID/response" \
    -d "$DATA"
}

# Report an error to the runtime API
process_invalid_payload() {
  REQUEST_ID=$1
  DATA_FILE=$2
  echo Unknown event data format $(cat "$DATA_FILE")
  DATA='{ "errorMessage": "Invalid event data", "errorType": "InvalidEventDataException" }'
  curl -s -X POST \
    "http://${AWS_LAMBDA_RUNTIME_API}/2018-06-01/runtime/invocation/$REQUEST_ID/error" \
    -d "$DATA" >/dev/null
}

# Get events from the runtime API and process them in a loop
start_runtime() {
  while true; do
    # get an event from the runtime API
    HEADERS="$(mktemp)"
    DATA_FILE="$(mktemp)"
    curl -sSL \
      "http://${AWS_LAMBDA_RUNTIME_API}/2018-06-01/runtime/invocation/next" \
      -D "$HEADERS" \
      -o "$DATA_FILE"

    # get request ID from headers
    REQUEST_ID=$(grep -i Lambda-Runtime-Aws-Request-Id "$HEADERS" | tr -d '[:space:]' | cut -d: -f2)

    if [ ! "$(jq -cr .Records < $DATA_FILE)" = "null" ]; then
      # asynchronous invoke from SQS
      for payload in $(get_event_payloads "$EVENT_DATA"); do
        process_payload "$REQUEST_ID" "$payload"
      done
    elif [ ! "$(jq -cr .command < $DATA_FILE)" = "null" ]; then
      # synchronous invoke
      process_payload "$REQUEST_ID" "$DATA_FILE"
    else
      process_invalid_payload "$REQUEST_ID" "$DATA_FILE"
    fi
  done
}

start_runtime