[DPE-1626] Add support for certificates and CA renewal

lib/charms/opensearch/v0/constants_charm.py

@@ -27,10 +27,9 @@
 ServiceStopped = "The OpenSearch service stopped."
 ServiceStopFailed = "An error occurred while attempting to stop the OpenSearch service."
 ServiceIsStopping = "The OpenSearch service is stopping."
+TLSRelationMissing = "The TLS operator is not related to OpenSearch. Cannot start this unit."
 TLSNotFullyConfigured = "Waiting for TLS to be fully configured..."
-TLSRelationBrokenError = (
-    "Relation broken with the TLS Operator while TLS not fully configured. Stopping OpenSearch."
-)
+TLSRelationBrokenError = "Relation broken with the TLS Operator while TLS not fully configured."
 NoNodeUpInCluster = "No node is up in this cluster."
 TooManyNodesRemoved = (
     "Too many nodes being removed at the same time, please scale your application up."

lib/charms/opensearch/v0/helper_commands.py

@@ -0,0 +1,59 @@
+# Copyright 2023 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+"""Utility functions for running commands."""
+
+import logging
+import os
+import subprocess
+from types import SimpleNamespace
+
+from charms.opensearch.v0.opensearch_exceptions import OpenSearchCmdError
+
+# The unique Charmhub library identifier, never change it
+LIBID = "f7199a359074406db94294bef78e3f2a"
+
+# Increment this major API version when introducing breaking changes
+LIBAPI = 0
+
+# Increment this PATCH version before using `charmcraft publish-lib` or reset
+# to 0 if you are raising the major API version
+LIBPATCH = 1
+
+
+logger = logging.getLogger(__name__)
+
+
+def run_cmd(command: str, args: str = None) -> SimpleNamespace:
+    """Run command.
+
+    Arg:
+        command: can contain arguments
+        args: command line arguments
+    """
+    if args is not None:
+        command = f"{command} {args}"
+
+    command = " ".join(command.split())
+
+    logger.debug(f"Executing command: {command}")
+
+    try:
+        output = subprocess.run(
+            command,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            shell=True,
+            text=True,
+            encoding="utf-8",
+            timeout=25,
+            env=os.environ,
+        )
+
+        if output.returncode != 0:
+            logger.error(f"err: {output.stderr} / out: {output.stdout}")
+            raise OpenSearchCmdError(cmd=command, out=output.stdout, err=output.stderr)
+
+        return SimpleNamespace(cmd=command, out=output.stdout, err=output.stderr)
+    except (TimeoutError, subprocess.TimeoutExpired):
+        raise OpenSearchCmdError(cmd=command)