feat!: parameterise snapshot admin username (#2)

# What this PR is

This PR parameterises the `db_snapshot_admin_username` parameter. This is because the `create_database_server` function internally was hardcoding the admin username of snapshots, which we discovered didn't align to our example in CSDA STAC API: NASA-IMPACT/csda-project#753 (comment)

With this change, we can now override this value so that when a DB is restored from a snapshot, its admin user just gets a new password generated and we don't lock ourselves out 🎉

As this is a breaking change (changed the default value to be the RDS default value _and_ parameterised it) I've bumped the version - Not sure how we release this, but looks like we just install via git url in the projects that use this.

# What I changed

* Bumped version in `VERSION`
* Added in `.flake8` just to reduce some linting issues (I envision in another workstream we actally give this repo some TLC in terms of dev tooling)
* Added a new example to the `README.md` for the above changes and removed some unused vars in the other examples
* Lint fixes in `cdk_bootstrapped_db/constructs.py`
* Parameterised `db_snapshot_admin_username` in `cdk_boostrapped_db/helpers.py:create_database_server`

# How you can test this

If you're using the `create_database_server` functionality with a snapshot, you should be able to install this new version and just provide `db_snapshot_admin_username` as the value of the admin user of the snapshot and you should get a cdk diff with no changes to that construct.

**Or** just watch this issue as we tackle it: NASA-IMPACT/csda-project#753

---------

Co-authored-by: Chris Holden <[email protected]>

Author: ciaransweet

.flake8

@@ -0,0 +1,2 @@
+[flake8]
+max-line-length=88

README.md

@@ -7,15 +7,13 @@ This CDK Construct enables provisioning an RDS Database (and optionally a DB Ser
 ```python
 import os
 from aws_cdk import (
-    Duration,
     aws_ec2 as ec2,
     aws_rds as rds,
     aws_lambda as lambda_,
 )
 
 from constructs import Construct
 
-from cdk_bootstrapped_db.helpers import create_database_server
 from cdk_bootstrapped_db.constructs import BootstrappedDb
 
 
@@ -24,7 +22,6 @@ class MyDatabase(Construct):
         self,
         scope: Construct,
         id: str,
-        name: str,
         secrets_prefix: str,
         db_server: rds.DatabaseInstance,
         vpc: ec2.IVpc,
@@ -66,7 +63,6 @@ This package comes with a helper function for setting up a new RDS server. The a
 ```python
 import os
 from aws_cdk import (
-    Duration,
     aws_ec2 as ec2,
     aws_rds as rds,
     aws_lambda as lambda_,
@@ -83,7 +79,6 @@ class MyDatabase(Construct):
         self,
         scope: Construct,
         id: str,
-        name: str,
         secrets_prefix: str,
         vpc: ec2.IVpc,
         **kwargs,
@@ -126,3 +121,79 @@ class MyDatabase(Construct):
 
         self.db_connection_secret = self.db.secret
 ```
+
+### Creating an RDS Server from a Snapshot
+
+If you have a snapshot of an RDS Server that you wish to restore in a new deployment, you can pass in the optional parameter
+`db_snapshot_arn` to `create_database_server` instead of using `db_name`.
+
+This snapshot must reside in the region you're deploying into, you can copy a snapshot across regions following these docs:
+https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_CopySnapshot.html
+
+By default, the created server will use the admin username of `postgres` - If the RDS Server your snapshot is from used a
+different admin username, you can provide it with the parameter `db_snapshot_admin_username`.
+
+This whole scenario is shown below:
+
+```python
+import os
+from aws_cdk import (
+    aws_ec2 as ec2,
+    aws_rds as rds,
+    aws_lambda as lambda_,
+)
+
+from constructs import Construct
+
+from cdk_bootstrapped_db.helpers import create_database_server
+from cdk_bootstrapped_db.constructs import BootstrappedDb
+
+
+class MyDatabase(Construct):
+    def __init__(
+        self,
+        scope: Construct,
+        id: str,
+        secrets_prefix: str,
+        vpc: ec2.IVpc,
+        **kwargs,
+    ):
+        super().__init__(scope, id, **kwargs)
+
+        self.db_server = create_database_server(
+            self,
+            "MyDBServer",
+            identifier="mydbserver",
+            vpc=vpc,
+            db_snapshot_arn="arn:aws:rds:us-west-2:123456789012:snapshot:mysql-instance1-snapshot-20130805",
+            db_snapshot_admin_username="myadminusername",
+            db_version=rds.PostgresEngineVersion.VER_14,
+            instance_type=ec2.InstanceType.of(
+                ec2.InstanceClass.BURSTABLE4_GRAVITON, ec2.InstanceSize.NANO
+            ),
+        )
+
+        db_setup_handler = lambda_.Function(
+            self,
+            "RunMigrations",
+            handler="handler.handler",
+            runtime=lambda_.Runtime.PYTHON_3_8,
+            code=lambda_.Code.from_docker_build(
+                path=os.path.abspath("."),
+                file="Dockerfile",
+            ),
+            vpc=vpc,
+        )
+
+        self.db = BootstrappedDb(
+            self,
+            "MyDB",
+            db=self.db_server,
+            new_dbname="mydb",
+            new_username="mydbuser",
+            secrets_prefix=secrets_prefix,
+            handler=db_setup_handler,
+        )
+
+        self.db_connection_secret = self.db.secret
+```

VERSION

@@ -1 +1 @@
-2.1.0
+3.0.0

cdk_bootstrapped_db/constructs.py

@@ -1,6 +1,5 @@
 import json
 import os
-from datetime import datetime
 from typing import Optional, Union
 
 from aws_cdk import (
@@ -56,7 +55,9 @@ def __init__(
                 secret_string_template=json.dumps(
                     {
                         "dbname": new_dbname,
-                        "engine": db_engine if db_engine else db.engine.engine_type,  # type: ignore
+                        "engine": db_engine
+                        if db_engine
+                        else db.engine.engine_type,  # type: ignore
                         "port": db.instance_endpoint.port,
                         "host": db.instance_endpoint.hostname,
                         "username": new_username,
@@ -83,7 +84,9 @@ def __init__(
                     secret_string_template=json.dumps(
                         {
                             "dbname": new_dbname,
-                            "engine": db_engine if db_engine else db.engine.engine_type,  # type: ignore
+                            "engine": db_engine
+                            if db_engine
+                            else db.engine.engine_type,  # type: ignore
                             "port": db.instance_endpoint.port,
                             "host": db.instance_endpoint.hostname,
                             "username": read_only_username,
@@ -92,7 +95,7 @@ def __init__(
                     generate_string_key="password",
                     exclude_punctuation=True,
                 ),
-                description=f"Read-only user secret deployed by {Stack.of(self).stack_name}",
+                description=f"Read-only user secret deployed by {Stack.of(self).stack_name}",  # noqa: E501
             )
 
         self.provider = custom_resources.Provider(
@@ -108,9 +111,9 @@ def __init__(
 
         # Optionally include the read-only secret ARN
         if self.read_only_secret:
-            resource_properties["read_only_user_secret_arn"] = (
-                self.read_only_secret.secret_arn
-            )
+            resource_properties[
+                "read_only_user_secret_arn"
+            ] = self.read_only_secret.secret_arn
 
         self.resource = CustomResource(
             scope=scope,

cdk_bootstrapped_db/helpers.py

@@ -11,6 +11,9 @@ def create_database_server(
     vpc: ec2.IVpc,
     subnet_selection: ec2.SubnetSelection,
     deletion_protect: bool,
+    # Default admin username for Postgres is "postgres" for rds.DatabaseInstance
+    # https://docs.aws.amazon.com/cdk/api/v2/python/aws_cdk.aws_rds/DatabaseInstance.html#aws_cdk.aws_rds.DatabaseInstance
+    db_snapshot_admin_username: str = "postgres",
     db_name: Optional[str] = None,
     db_snapshot_arn: Optional[str] = None,
     db_version: Optional[rds.PostgresEngineVersion] = None,
@@ -51,7 +54,7 @@ def create_database_server(
             **params,
             snapshot_identifier=db_snapshot_arn,
             credentials=rds.SnapshotCredentials.from_generated_password(
-                username="superuser"
+                username=db_snapshot_admin_username
             ),
         )