s3-monitor

s3-monitor is a small serverless app that checks an S3 prefix once a day and emails you (via SES) if the most recent object under that prefix is not from today. Useful for backup-freshness alerting (home automation snapshots, database dumps, etc.).

How it works

• A single AWS Lambda function (Python 3.12, arm64) lists the configured bucket/prefix and finds the object with the most recent LastModified timestamp.
• If that date is today, it stays silent.
• If it is stale or there are no objects at all, it sends an SES email to the configured recipient list.
• A CloudWatch alarm on the function's ERROR log lines publishes to an SNS topic so a single on-call address gets paged if the function itself fails.
• A daily EventBridge schedule (via SAM's Schedule event) triggers the function. The schedule can be disabled per environment via the CRONENABLED parameter.

Requirements

• AWS account with SES in production mode (or sandbox if SENDER and all RECIPIENTS are verified).
• AWS CLI v2 and AWS SAM CLI installed locally.
• Python 3.12 (for tests/lint only; the runtime ships its own).
• Configured AWS credentials. aws-vault recommended.

Deploy

The only supported deploy path is SAM. Configuration for the dev and prod stacks lives in samconfig.toml.

The first time, you'll need to supply the SES-related parameters either via --parameter-overrides or by editing samconfig.toml. The mandatory parameters are:

Parameter	Description
MONITORINGBUCKET	The bucket to inspect
S3PREFIX	Key prefix to scope the listing (use empty string for whole bucket)
SENDER	SES-verified sender address
RECIPIENTS	Whitespace-separated list of SES recipient addresses
ALERTRECIPIENT	Single email subscribed to the function's error SNS topic

make build
make deploy ENV=dev \
  # or: sam deploy --config-env dev \
  #   --parameter-overrides "MONITORINGBUCKET=..." "SENDER=..." \
  #                         "RECIPIENTS='a@x b@y'" "ALERTRECIPIENT=ops@x"

To tear a stack down:

make destroy ENV=dev

Develop

python3.12 -m venv .venv
source .venv/bin/activate
pip install -r requirements-dev.txt

make lint   # ruff check .
make test   # pytest

Tests run against moto and do not touch AWS.

License

MIT. See LICENSE.