feat(DPE-5371): Storage reuse on a different cluster

Features:
 * Storage reuse on the same cluster (scale down, scale to zero)
 * Storage reuse on a different cluster with same app name
 * Storage reuse on a different cluster with different app name

lib/charms/mongodb/v0/mongo.py

@@ -31,7 +31,7 @@ class NotReadyError(PyMongoError):
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 1
+LIBPATCH = 2
 
 ADMIN_AUTH_SOURCE = "authSource=admin"
 SYSTEM_DBS = ("admin", "local", "config")
@@ -270,6 +270,11 @@ def get_users(self) -> Set[str]:
             ]
         )
 
+    def get_all_users(self) -> Set[str]:
+        """Get all users, including the three charmed managed users."""
+        users_info = self.client.admin.command("usersInfo")
+        return {user_obj["user"] for user_obj in users_info["users"]}
+
     def get_databases(self) -> Set[str]:
         """Return list of all non-default databases."""
         databases = self.client.list_database_names()
@@ -280,3 +285,7 @@ def drop_database(self, database: str):
         if database in SYSTEM_DBS:
             return
         self.client.drop_database(database)
+
+    def drop_local_database(self):
+        """DANGEROUS: Drops the local database."""
+        self.client.drop_database("local")

lib/charms/mongodb/v1/helpers.py

@@ -23,7 +23,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 10
+LIBPATCH = 11
 
 # path to store mongodb ketFile
 KEY_FILE = "keyFile"
@@ -176,6 +176,8 @@ def get_mongod_args(
     auth: bool = True,
     snap_install: bool = False,
     role: str = "replication",
+    machine_ip: str = "127.0.0.1",
+    degraded: bool = False,
 ) -> str:
     """Construct the MongoDB startup command line.
 
@@ -186,6 +188,24 @@ def get_mongod_args(
     full_conf_dir = f"{MONGODB_SNAP_DATA_DIR}{CONF_DIR}" if snap_install else CONF_DIR
     logging_options = _get_logging_options(snap_install)
     audit_log_settings = _get_audit_log_settings(snap_install)
+    if degraded:
+        cmd = [
+            # Only bind to local IP
+            f"--bind_ip {machine_ip}",
+            # db must be located within the snap common directory since the
+            # snap is strictly confined
+            f"--dbpath={full_data_dir}",
+            # for simplicity we run the mongod daemon on shards, configsvrs,
+            # and replicas on the same port
+            f"--port={Config.MONGODB_PORT}",
+            "--setParameter processUmask=037",  # required for log files perminission (g+r)
+            "--logRotate reopen",
+            "--logappend",
+            logging_options,
+            "--setParameter enableLocalhostAuthBypass=0",
+            "\n",
+        ]
+        return " ".join(cmd)
     cmd = [
         # bind to localhost and external interfaces
         "--bind_ip_all",
@@ -266,6 +286,15 @@ def generate_keyfile() -> str:
     return "".join([secrets.choice(choices) for _ in range(1024)])
 
 
+def generate_lock_hash() -> str:
+    """Lock hash used to check if we are reusing storage in a different context or not.
+
+    Returns:
+       An 8 character random hexadecimal string.
+    """
+    return secrets.token_hex(8)
+
+
 def copy_licenses_to_unit():
     """Copies licenses packaged in the snap to the charm's licenses directory."""
     os.makedirs("src/licenses", exist_ok=True)

lib/charms/mongodb/v1/mongodb.py

@@ -4,7 +4,7 @@
 # See LICENSE file for licensing details.
 
 import logging
-from typing import Dict, Set
+from typing import Dict, Set, Tuple
 
 from bson.json_util import dumps
 from charms.mongodb.v0.mongo import MongoConfiguration, MongoConnection, NotReadyError
@@ -27,7 +27,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 3
+LIBPATCH = 4
 
 # path to store mongodb ketFile
 logger = logging.getLogger(__name__)
@@ -95,6 +95,35 @@ def init_replset(self) -> None:
                 #     finished.
                 logger.error("Cannot initialize replica set. error=%r", e)
                 raise e
+            else:
+                logger.error("Error in init %s", e)
+
+    @retry(
+        stop=stop_after_attempt(3),
+        wait=wait_fixed(5),
+        reraise=True,
+        before=before_log(logger, logging.DEBUG),
+    )
+    def reconfigure_replset(self, hosts: set[str], version: int, force: bool = False) -> None:
+        """Create replica set config the first time.
+
+        Raises:
+            ConfigurationError, ConfigurationError, OperationFailure
+        """
+        config = {
+            "_id": self.config.replset,
+            "members": [{"_id": i, "host": h} for i, h in enumerate(hosts)],
+            "version": version,
+        }
+        try:
+            self.client.admin.command("replSetReconfig", config, force=force)
+        except OperationFailure as e:
+            # Unauthorized error can be raised only if initial user were
+            #     created the step after this.
+            # AlreadyInitialized error can be raised only if this step
+            #     finished.
+            logger.error("Cannot reconfigure replica set. error=%r", e)
+            raise e
 
     def get_replset_status(self) -> Dict:
         """Get a replica set status as a dict.
@@ -128,6 +157,17 @@ def get_replset_members(self) -> Set[str]:
         ]
         return set(curr_members)
 
+    def get_replset_members_and_version(self) -> Tuple[Set[str], int]:
+        """Get replica set members through config."""
+        rs_config = self.client.admin.command("replSetGetConfig")
+        curr_members = [
+            self._hostname_from_hostport(member["host"])
+            for member in rs_config["config"]["members"]
+        ]
+        version = rs_config["config"]["version"]
+
+        return set(curr_members), version
+
     def add_replset_member(self, hostname: str) -> None:
         """Add a new member to replica set config inside MongoDB.