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RDSMariaDB-Multiuser.py

Lambda rotation for AWS Secrets Manager - RDS MariaDB with separate Master secret

#snippet-sourceauthor: [aws] # Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved. # SPDX-License-Identifier: MIT-0 import boto3 import json import logging import os import pymysql logger = logging.getLogger() logger.setLevel(logging.INFO) def lambda_handler(event, context): """Secrets Manager RDS MariaDB Handler This handler uses the master-user rotation scheme to rotate an RDS MariaDB user credential. During the first rotation, this scheme logs into the database as the master user, creates a new user (appending _clone to the username), and grants the new user all of the permissions from the user being rotated. Once the secret is in the state, every subsequent rotation simply creates a new secret with the AWSPREVIOUS user credentials, adds any missing permissions that are in the current secret, changes that user's password, and then marks the latest secret as AWSCURRENT. The Secret SecretString is expected to be a JSON string with the following format: { 'engine': <required: must be set to 'mariadb'>, 'host': <required: instance host name>, 'username': <required: username>, 'password': <required: password>, 'dbname': <optional: database name>, 'port': <optional: if not specified, default port 3306 will be used>, 'masterarn': <required: the arn of the master secret which will be used to create users/change passwords> } Args: event (dict): Lambda dictionary of event parameters. These keys must include the following: - SecretId: The secret ARN or identifier - ClientRequestToken: The ClientRequestToken of the secret version - Step: The rotation step (one of createSecret, setSecret, testSecret, or finishSecret) context (LambdaContext): The Lambda runtime information Raises: ResourceNotFoundException: If the secret with the specified arn and stage does not exist ValueError: If the secret is not properly configured for rotation KeyError: If the secret json does not contain the expected keys """ arn = event['SecretId'] token = event['ClientRequestToken'] step = event['Step'] # Setup the client service_client = boto3.client('secretsmanager', endpoint_url=os.environ['SECRETS_MANAGER_ENDPOINT']) # Make sure the version is staged correctly metadata = service_client.describe_secret(SecretId=arn) if "RotationEnabled" in metadata and not metadata['RotationEnabled']: logger.error("Secret %s is not enabled for rotation" % arn) raise ValueError("Secret %s is not enabled for rotation" % arn) versions = metadata['VersionIdsToStages'] if token not in versions: logger.error("Secret version %s has no stage for rotation of secret %s." % (token, arn)) raise ValueError("Secret version %s has no stage for rotation of secret %s." % (token, arn)) if "AWSCURRENT" in versions[token]: logger.info("Secret version %s already set as AWSCURRENT for secret %s." % (token, arn)) return elif "AWSPENDING" not in versions[token]: logger.error("Secret version %s not set as AWSPENDING for rotation of secret %s." % (token, arn)) raise ValueError("Secret version %s not set as AWSPENDING for rotation of secret %s." % (token, arn)) # Call the appropriate step if step == "createSecret": create_secret(service_client, arn, token) elif step == "setSecret": set_secret(service_client, arn, token) elif step == "testSecret": test_secret(service_client, arn, token) elif step == "finishSecret": finish_secret(service_client, arn, token) else: logger.error("lambda_handler: Invalid step parameter %s for secret %s" % (step, arn)) raise ValueError("Invalid step parameter %s for secret %s" % (step, arn)) def create_secret(service_client, arn, token): """Generate a new secret This method first checks for the existence of a secret for the passed in token. If one does not exist, it will generate a new secret and save it using the passed in token. Args: service_client (client): The secrets manager service client arn (string): The secret ARN or other identifier token (string): The ClientRequestToken associated with the secret version Raises: ValueError: If the current secret is not valid JSON KeyError: If the secret json does not contain the expected keys """ # Make sure the current secret exists current_dict = get_secret_dict(service_client, arn, "AWSCURRENT") # Now try to get the secret version, if that fails, put a new secret try: get_secret_dict(service_client, arn, "AWSPENDING", token) logger.info("createSecret: Successfully retrieved secret for %s." % arn) except service_client.exceptions.ResourceNotFoundException: # Get the alternate username swapping between the original user and the user with _clone appended to it current_dict['username'] = get_alt_username(current_dict['username']) # Generate a random password passwd = service_client.get_random_password(ExcludeCharacters='/@"\'\\') current_dict['password'] = passwd['RandomPassword'] # Put the secret service_client.put_secret_value(SecretId=arn, ClientRequestToken=token, SecretString=json.dumps(current_dict), VersionStages=['AWSPENDING']) logger.info("createSecret: Successfully put secret for ARN %s and version %s." % (arn, token)) def set_secret(service_client, arn, token): """Set the pending secret in the database This method tries to login to the database with the AWSPENDING secret and returns on success. If that fails, it tries to login with the master credentials from the masterarn in the current secret. If this succeeds, it adds all grants for AWSCURRENT user to the AWSPENDING user, creating the user and/or setting the password in the process. Else, it throws a ValueError. Args: service_client (client): The secrets manager service client arn (string): The secret ARN or other identifier token (string): The ClientRequestToken associated with the secret version Raises: ResourceNotFoundException: If the secret with the specified arn and stage does not exist ValueError: If the secret is not valid JSON or master credentials could not be used to login to DB KeyError: If the secret json does not contain the expected keys """ # First try to login with the pending secret, if it succeeds, return pending_dict = get_secret_dict(service_client, arn, "AWSPENDING", token) conn = get_connection(pending_dict) if conn: conn.close() logger.info("setSecret: AWSPENDING secret is already set as password in MariaDB DB for secret arn %s." % arn) return # Before we do anything with the secret, make sure the AWSCURRENT secret is valid by logging in to the db current_dict = get_secret_dict(service_client, arn, "AWSCURRENT") conn = get_connection(current_dict) if not conn: logger.error("setSecret: Unable to log into database using current credentials for secret %s" % arn) raise ValueError("Unable to log into database using current credentials for secret %s" % arn) conn.close() # Now get the master arn from the current secret master_arn = current_dict['masterarn'] master_dict = get_secret_dict(service_client, master_arn, "AWSCURRENT") if current_dict['host'] != master_dict['host']: logger.warn("setSecret: Master database host %s is not the same host as current %s" % (master_dict['host'], current_dict['host'])) # Now log into the database with the master credentials conn = get_connection(master_dict) if not conn: logger.error("setSecret: Unable to log into database using credentials in master secret %s" % master_arn) raise ValueError("Unable to log into database using credentials in master secret %s" % master_arn) # Now set the password to the pending password try: with conn.cursor() as cur: # List the grants on the current user and add them to the pending user. # This also creates the user if it does not already exist cur.execute("SHOW GRANTS FOR %s", current_dict['username']) for row in cur.fetchall(): grant = row[0].split(' TO ') new_grant = "%s TO %s" % (grant[0], pending_dict['username']) cur.execute(new_grant + " IDENTIFIED BY %s", pending_dict['password']) conn.commit() logger.info("setSecret: Successfully set password for %s in MariaDB DB for secret arn %s." % (pending_dict['username'], arn)) finally: conn.close() def test_secret(service_client, arn, token): """Test the pending secret against the database This method tries to log into the database with the secrets staged with AWSPENDING and runs a permissions check to ensure the user has the correct permissions. Args: service_client (client): The secrets manager service client arn (string): The secret ARN or other identifier token (string): The ClientRequestToken associated with the secret version Raises: ResourceNotFoundException: If the secret with the specified arn and stage does not exist ValueError: If the secret is not valid JSON or pending credentials could not be used to login to the database KeyError: If the secret json does not contain the expected keys """ # Try to login with the pending secret, if it succeeds, return conn = get_connection(get_secret_dict(service_client, arn, "AWSPENDING", token)) if conn: # This is where the lambda will validate the user's permissions. Modify the below lines to # tailor these validations to your needs try: with conn.cursor() as cur: cur.execute("SELECT NOW()") conn.commit() finally: conn.close() logger.info("testSecret: Successfully signed into MariaDB DB with AWSPENDING secret in %s." % arn) return else: logger.error("testSecret: Unable to log into database with pending secret of secret ARN %s" % arn) raise ValueError("Unable to log into database with pending secret of secret ARN %s" % arn) def finish_secret(service_client, arn, token): """Finish the rotation by marking the pending secret as current This method moves the secret from the AWSPENDING stage to the AWSCURRENT stage. Args: service_client (client): The secrets manager service client arn (string): The secret ARN or other identifier token (string): The ClientRequestToken associated with the secret version Raises: ResourceNotFoundException: If the secret with the specified arn and stage does not exist """ # First describe the secret to get the current version metadata = service_client.describe_secret(SecretId=arn) current_version = None for version in metadata["VersionIdsToStages"]: if "AWSCURRENT" in metadata["VersionIdsToStages"][version]: if version == token: # The correct version is already marked as current, return logger.info("finishSecret: Version %s already marked as AWSCURRENT for %s" % (version, arn)) return current_version = version break # Finalize by staging the secret version current service_client.update_secret_version_stage(SecretId=arn, VersionStage="AWSCURRENT", MoveToVersionId=token, RemoveFromVersionId=current_version) logger.info("finishSecret: Successfully set AWSCURRENT stage to version %s for secret %s." % (version, arn)) def get_connection(secret_dict): """Gets a connection to MariaDB DB from a secret dictionary This helper function tries to connect to the database grabbing connection info from the secret dictionary. If successful, it returns the connection, else None Args: secret_dict (dict): The Secret Dictionary Returns: Connection: The pymysql.connections.Connection object if successful. None otherwise Raises: KeyError: If the secret json does not contain the expected keys """ port = int(secret_dict['port']) if 'port' in secret_dict else 3306 dbname = secret_dict['dbname'] if 'dbname' in secret_dict else None # Try to obtain a connection to the db try: conn = pymysql.connect(secret_dict['host'], user=secret_dict['username'], passwd=secret_dict['password'], port=port, db=dbname, connect_timeout=5) return conn except pymysql.OperationalError: return None def get_secret_dict(service_client, arn, stage, token=None): """Gets the secret dictionary corresponding for the secret arn, stage, and token This helper function gets credentials for the arn and stage passed in and returns the dictionary by parsing the JSON string Args: service_client (client): The secrets manager service client arn (string): The secret ARN or other identifier token (string): The ClientRequestToken associated with the secret version, or None if no validation is desired stage (string): The stage identifying the secret version Returns: SecretDictionary: Secret dictionary Raises: ResourceNotFoundException: If the secret with the specified arn and stage does not exist ValueError: If the secret is not valid JSON """ required_fields = ['host', 'username', 'password'] # Only do VersionId validation against the stage if a token is passed in if token: secret = service_client.get_secret_value(SecretId=arn, VersionId=token, VersionStage=stage) else: secret = service_client.get_secret_value(SecretId=arn, VersionStage=stage) plaintext = secret['SecretString'] secret_dict = json.loads(plaintext) # Run validations against the secret if 'engine' not in secret_dict or secret_dict['engine'] != 'mariadb': raise KeyError("Database engine must be set to 'mariadb' in order to use this rotation lambda") for field in required_fields: if field not in secret_dict: raise KeyError("%s key is missing from secret JSON" % field) # Parse and return the secret JSON string return secret_dict def get_alt_username(current_username): """Gets the alternate username for the current_username passed in This helper function gets the username for the alternate user based on the passed in current username. Args: current_username (client): The current username Returns: AlternateUsername: Alternate username Raises: ValueError: If the new username length would exceed the maximum allowed """ clone_suffix = "_clone" if current_username.endswith(clone_suffix): return current_username[:(len(clone_suffix) * -1)] else: new_username = current_username + clone_suffix if len(new_username) > 80: raise ValueError("Unable to clone user, username length with _clone appended would exceed 80 characters") return new_username

Sample Details

Service: secretsmanager

Last tested: 2018-08-22

Type: full-example

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