Persistence

By default, AWSim is stateless — all data lives in memory and is lost when the process exits. Enable persistence with --data-dir.

Enabling Persistence

./awsim --data-dir /var/lib/awsim
# or
AWSIM_DATA_DIR=/var/lib/awsim ./awsim

AWSim creates the directory if it does not exist.

Services That Persist

The following services write and restore snapshots:

Service	Signing Name
SQS	sqs
DynamoDB	dynamodb
IAM	iam
S3	s3
RDS	rds
Cognito User Pools	cognito-idp
Cognito Identity Pools	cognito-identity
ACM	acm
WAF	wafv2
Scheduler	scheduler
SNS	sns

Services not in this list (e.g., Lambda, KMS, Secrets Manager) are always in-memory only.

Note on S3: S3 bucket metadata and object metadata are persisted, but object data (the actual bytes) is not. After a restart, the bucket and object listings will be restored but GetObject will return empty content for previously stored objects.

Snapshot Format

Snapshots are written to {data_dir}/snapshots/ as JSON files, one per service:

/var/lib/awsim/
  snapshots/
    s3.json
    dynamodb.json
    sqs.json
    iam.json
    ...

Auto-Save

AWSim saves snapshots every 30 seconds while running.

Graceful Shutdown

When AWSim receives SIGINT (Ctrl+C) or SIGTERM, it saves all snapshots before exiting. This ensures data written in the last interval is not lost.

Atomic Writes

Snapshots are written atomically: AWSim writes to a temporary file first, then renames it to the final path. This prevents corrupt snapshots from a mid-write crash.

Restoring State

On startup, AWSim reads each {data_dir}/snapshots/{service}.json file and restores the service state. If a snapshot file is missing or malformed, AWSim starts that service with empty state and logs a warning.