Stream stdin to cloudwatch logs

stream-to-cw-logs

#!/bin/bash

# Enable bash strict mode
set -euo pipefail
IFS=$'\n\t'

# Disable the pager for aws commands (no less on the host)
export AWS_PAGER=""

# Get the log group arn as a parameter and cut the group name out of it
# Looks like arn:aws:logs:us-west-2:123456789012:log-group:/my/log/group
log_group_arn="$1"
log_group=$(echo "${log_group_arn}" | awk -F ':log-group:' '{print $2}')
log_stream="$(/usr/local/bin/bk-ec2-instance-meta-data instance-id)"

# Ensure the log stream exists, create if it doesn't
log_stream_exists=$(aws logs describe-log-streams --log-group-name "${log_group}" \
  --log-stream-name-prefix "${log_stream}" \
  --query 'logStreams[?logStreamName==`'"${log_stream}"'`].logStreamName' \
  --output text)

if [ -z "$log_stream_exists" ]; then
  aws logs create-log-stream --log-group-name "${log_group}" \
    --log-stream-name "${log_stream}" || { echo >&2 "Failed to create log stream."; exit 1; }
fi

# Function to send a message to CloudWatch Logs
send_message_to_logs() {
  local message="${1}"
  local sequence_token
  sequence_token=$(aws logs describe-log-streams \
    --log-group-name "${log_group}" \
    --log-stream-name-prefix "${log_stream}" \
    --query 'logStreams[0].uploadSequenceToken' \
    --output text)

  # Remove trailing newline characters
  message=$(echo -n "$message" | tr -d '\n')

  # Use json encoding for the message to escape chars that cause issues
  local json_message
  json_message=$(jq -aRs . <<< "$message")

  if [ "$sequence_token" = "None" ]; then
    aws logs put-log-events \
      --log-group-name "${log_group}" \
      --log-stream-name "${log_stream}" \
      --log-events "timestamp=$(date +%s000),message=${json_message}"
  else
    aws logs put-log-events \
      --log-group-name "${log_group}" \
      --log-stream-name "${log_stream}" \
      --log-events "timestamp=$(date +%s000),message=${json_message}" \
      --sequence-token "$sequence_token"
  fi
}

# Read stdin and send each line to CloudWatch Logs
while IFS= read -r line; do
  send_message_to_logs "${line}"
done