[DPE-3297] Display audit logs in Canonical Observability Stack (#337)

## Issue
A user\admin should be able to see audit logs in CoS

## Solution
As a first iteration of the feature - write audit logs to syslog 

<img width="1918" alt="Screenshot 2024-01-17 at 17 32 26"
src="https://github.com/canonical/mongodb-operator/assets/132273757/56be76fe-6233-4c88-818b-70cd14b1aba1">


<img width="1812" alt="Screenshot 2024-01-17 at 17 34 08"
src="https://github.com/canonical/mongodb-operator/assets/132273757/f45a7270-e100-454b-80af-707aeb52745e">

lib/charms/mongodb/v1/helpers.py

@@ -29,7 +29,7 @@
 
 # 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
 
 # path to store mongodb ketFile
 KEY_FILE = "keyFile"
@@ -44,11 +44,22 @@
 MONGO_SHELL = "charmed-mongodb.mongosh"
 
 DATA_DIR = "/var/lib/mongodb"
+LOG_DIR = "/var/log/mongodb"
+LOG_TO_SYSLOG = True
 CONF_DIR = "/etc/mongod"
 MONGODB_LOG_FILENAME = "mongodb.log"
 logger = logging.getLogger(__name__)
 
 
+def _get_logging_options(snap_install: bool) -> str:
+    # TODO sending logs to syslog until we have a separate mount point for logs
+    if LOG_TO_SYSLOG:
+        return ""
+    # in k8s the default logging options that are used for the vm charm are ignored and logs are
+    # the output of the container. To enable logging to a file it must be set explicitly
+    return f"--logpath={LOG_DIR}/{MONGODB_LOG_FILENAME}" if snap_install else ""
+
+
 # noinspection GrazieInspection
 def get_create_user_cmd(config: MongoDBConfiguration, mongo_path=MONGO_SHELL) -> List[str]:
     """Creates initial admin user for MongoDB.
@@ -130,9 +141,7 @@ def get_mongod_args(
     """
     full_data_dir = f"{MONGODB_COMMON_DIR}{DATA_DIR}" if snap_install else DATA_DIR
     full_conf_dir = f"{MONGODB_SNAP_DATA_DIR}{CONF_DIR}" if snap_install else CONF_DIR
-    # in k8s the default logging options that are used for the vm charm are ignored and logs are
-    # the output of the container. To enable logging to a file it must be set explicitly
-    logging_options = "" if snap_install else f"--logpath={full_data_dir}/{MONGODB_LOG_FILENAME}"
+    logging_options = _get_logging_options(snap_install)
     cmd = [
         # bind to localhost and external interfaces
         "--bind_ip_all",
@@ -143,9 +152,8 @@ def get_mongod_args(
         # for simplicity we run the mongod daemon on shards, configsvrs, and replicas on the same
         # port
         f"--port={Config.MONGODB_PORT}",
-        "--auditDestination=file",
+        "--auditDestination=syslog",  # TODO sending logs to syslog until we have a separate mount point for logs
         f"--auditFormat={Config.AuditLog.FORMAT}",
-        f"--auditPath={full_data_dir}/{Config.AuditLog.FILE_NAME}",
         logging_options,
     ]
     if auth:

src/config.py

@@ -16,7 +16,7 @@ class Config:
     MONGODB_SNAP_DATA_DIR = "/var/snap/charmed-mongodb/current"
     MONGOD_CONF_DIR = f"{MONGODB_SNAP_DATA_DIR}/etc/mongod"
     MONGOD_CONF_FILE_PATH = f"{MONGOD_CONF_DIR}/mongod.conf"
-    SNAP_PACKAGES = [("charmed-mongodb", "6/edge", 87)]
+    SNAP_PACKAGES = [("charmed-mongodb", "6/edge", 93)]
 
     # Keep these alphabetically sorted
     class Actions:
@@ -29,7 +29,7 @@ class AuditLog:
         """Audit log related configuration."""
 
         FORMAT = "JSON"
-        FILE_NAME = "audit.json"
+        FILE_NAME = "audit.log"
 
     class Backup:
         """Backup related config for MongoDB Charm."""

tests/integration/test_charm.py

@@ -340,11 +340,12 @@ def juju_reports_one_primary(unit_messages):
     await ops_test.model.destroy_unit(target_unit)
 
 
+@pytest.mark.skip("Skipping until write to log files enabled")
 async def test_audit_log(ops_test: OpsTest) -> None:
     """Test that audit log was created and contains actual audit data."""
     app_name = await get_app_name(ops_test)
     leader_unit = await find_unit(ops_test, leader=True, app_name=app_name)
-    audit_log_snap_path = "/var/snap/charmed-mongodb/common/var/lib/mongodb/audit.json"
+    audit_log_snap_path = "/var/snap/charmed-mongodb/common/var/log/mongodb/audit.log"
     audit_log = check_output(
         f"JUJU_MODEL={ops_test.model_full_name} juju ssh {leader_unit.name} 'sudo cat {audit_log_snap_path}'",
         stderr=subprocess.PIPE,

tests/unit/test_mongodb_helpers.py

@@ -14,9 +14,8 @@ def test_get_mongod_args(self):
             "--replSet=my_repl_set",
             "--dbpath=/var/snap/charmed-mongodb/common/var/lib/mongodb",
             "--port=27017",
-            "--auditDestination=file",
+            "--auditDestination=syslog",
             "--auditFormat=JSON",
-            "--auditPath=/var/snap/charmed-mongodb/common/var/lib/mongodb/audit.json",
             "--auth",
             "--clusterAuthMode=keyFile",
             "--keyFile=/var/snap/charmed-mongodb/current/etc/mongod/keyFile",
@@ -39,9 +38,8 @@ def test_get_mongod_args(self):
             "--replSet=my_repl_set",
             "--dbpath=/var/snap/charmed-mongodb/common/var/lib/mongodb",
             "--port=27017",
-            "--auditDestination=file",
+            "--auditDestination=syslog",
             "--auditFormat=JSON",
-            "--auditPath=/var/snap/charmed-mongodb/common/var/lib/mongodb/audit.json",
         ]
 
         self.assertEqual(
@@ -56,10 +54,8 @@ def test_get_mongod_args(self):
             "--replSet=my_repl_set",
             "--dbpath=/var/lib/mongodb",
             "--port=27017",
-            "--auditDestination=file",
+            "--auditDestination=syslog",
             "--auditFormat=JSON",
-            "--auditPath=/var/lib/mongodb/audit.json",
-            "--logpath=/var/lib/mongodb/mongodb.log",
         ]
 
         self.assertEqual(