Refresh CSR "whenever" needed (#110)

* refresh csr if needed

* use stable hash

* static

* sort sans

* lint

* comments

lib/charms/observability_libs/v1/cert_handler.py

@@ -32,6 +32,7 @@
 Since this library uses [Juju Secrets](https://juju.is/docs/juju/secret) it requires Juju >= 3.0.3.
 """
 import abc
+import hashlib
 import ipaddress
 import json
 import socket
@@ -67,7 +68,7 @@
 
 LIBID = "b5cd5cd580f3428fa5f59a8876dcbe6a"
 LIBAPI = 1
-LIBPATCH = 13
+LIBPATCH = 14
 
 VAULT_SECRET_LABEL = "cert-handler-private-vault"
 
@@ -301,14 +302,11 @@ def __init__(
                 Must match metadata.yaml.
             cert_subject: Custom subject. Name collisions are under the caller's responsibility.
             sans: DNS names. If none are given, use FQDN.
-            refresh_events: an optional list of bound events which
-                will be observed to replace the current CSR with a new one
-                if there are changes in the CSR's DNS SANs or IP SANs.
-                Then, subsequently, replace its corresponding certificate with a new one.
+            refresh_events: [DEPRECATED].
         """
         super().__init__(charm, key)
         # use StoredState to store the hash of the CSR
-        # to potentially trigger a CSR renewal on `refresh_events`
+        # to potentially trigger a CSR renewal
         self._stored.set_default(
             csr_hash=None,
         )
@@ -320,8 +318,9 @@ def __init__(
 
         # Use fqdn only if no SANs were given, and drop empty/duplicate SANs
         sans = list(set(filter(None, (sans or [socket.getfqdn()]))))
-        self.sans_ip = list(filter(is_ip_address, sans))
-        self.sans_dns = list(filterfalse(is_ip_address, sans))
+        # sort SANS lists to avoid unnecessary csr renewals during reconciliation
+        self.sans_ip = sorted(filter(is_ip_address, sans))
+        self.sans_dns = sorted(filterfalse(is_ip_address, sans))
 
         if self._check_juju_supports_secrets():
             vault_backend = _SecretVaultBackend(charm, secret_label=VAULT_SECRET_LABEL)
@@ -367,13 +366,15 @@ def __init__(
         )
 
         if refresh_events:
-            for ev in refresh_events:
-                self.framework.observe(ev, self._on_refresh_event)
+            logger.warn(
+                "DEPRECATION WARNING. `refresh_events` is now deprecated. CertHandler will automatically refresh the CSR when necessary."
+            )
 
-    def _on_refresh_event(self, _):
-        """Replace the latest current CSR with a new one if there are any SANs changes."""
-        if self._stored.csr_hash != self._csr_hash:
-            self._generate_csr(renew=True)
+        self._reconcile()
+
+    def _reconcile(self):
+        """Run all logic that is independent of what event we're processing."""
+        self._refresh_csr_if_needed()
 
     def _on_upgrade_charm(self, _):
         has_privkey = self.vault.get_value("private-key")
@@ -388,6 +389,11 @@ def _on_upgrade_charm(self, _):
             # this will call `self.private_key` which will generate a new privkey.
             self._generate_csr(renew=True)
 
+    def _refresh_csr_if_needed(self):
+        """Refresh the current CSR with a new one if there are any SANs changes."""
+        if self._stored.csr_hash is not None and self._stored.csr_hash != self._csr_hash:
+            self._generate_csr(renew=True)
+
     def _migrate_vault(self):
         peer_backend = _RelationVaultBackend(self.charm, relation_name="peers")
 
@@ -440,13 +446,17 @@ def enabled(self) -> bool:
         return True
 
     @property
-    def _csr_hash(self) -> int:
+    def _csr_hash(self) -> str:
         """A hash of the config that constructs the CSR.
 
         Only include here the config options that, should they change, should trigger a renewal of
         the CSR.
         """
-        return hash(
+
+        def _stable_hash(data):
+            return hashlib.sha256(str(data).encode()).hexdigest()
+
+        return _stable_hash(
             (
                 tuple(self.sans_dns),
                 tuple(self.sans_ip),

tests/scenario/test_cert_handler/test_cert_handler_v1.py

@@ -4,7 +4,7 @@
 import sys
 from contextlib import contextmanager
 from pathlib import Path
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 
 import pytest
 from cryptography import x509
@@ -36,7 +36,7 @@ def __init__(self, fw):
         if hostname := self._mock_san:
             sans.append(hostname)
 
-        self.ch = CertHandler(self, key="ch", sans=sans, refresh_events=[self.on.config_changed])
+        self.ch = CertHandler(self, key="ch", sans=sans)
 
     @property
     def _mock_san(self):
@@ -145,6 +145,14 @@ def _cert_renew_patch():
         yield patcher
 
 
+@contextmanager
+def _cert_generate_patch():
+    with patch(
+        "charms.tls_certificates_interface.v3.tls_certificates.TLSCertificatesRequiresV3.request_certificate_creation"
+    ) as patcher:
+        yield patcher
+
+
 @pytest.mark.parametrize("leader", (True, False))
 def test_cert_joins(ctx, certificates, leader):
     with ctx.manager(
@@ -183,48 +191,56 @@ def test_cert_joins_peer_vault_backend(ctx_juju2, certificates, leader):
         assert mgr.charm.ch.private_key
 
 
-def test_renew_csr_on_sans_change(ctx, certificates):
-    # generate a CSR
+# CertHandler generates a cert on `config_changed` event
+@pytest.mark.parametrize(
+    "event,expected_generate_calls",
+    (("update_status", 0), ("start", 0), ("install", 0), ("config_changed", 1)),
+)
+def test_no_renew_if_no_initial_csr_was_generated(
+    event, expected_generate_calls, ctx, certificates
+):
+    with _cert_renew_patch() as renew_patch:
+        with _cert_generate_patch() as generate_patch:
+            with ctx.manager(
+                event,
+                State(leader=True, relations=[certificates]),
+            ) as mgr:
+
+                mgr.run()
+                assert renew_patch.call_count == 0
+                assert generate_patch.call_count == expected_generate_calls
+
+
+@patch.object(CertHandler, "_stored", MagicMock())
+@pytest.mark.parametrize(
+    "is_relation, event",
+    (
+        (False, "start"),
+        (True, "changed_event"),
+        (False, "config_changed"),
+    ),
+)
+def test_csr_renew_on_any_event(is_relation, event, ctx, certificates):
     with ctx.manager(
-        certificates.joined_event,
-        State(leader=True, relations=[certificates]),
+        getattr(certificates, event) if is_relation else event,
+        State(
+            leader=True,
+            relations=[certificates],
+        ),
     ) as mgr:
         charm = mgr.charm
         state_out = mgr.run()
         orig_csr = get_csr_obj(charm.ch._csr)
         assert get_sans_from_csr(orig_csr) == {socket.getfqdn()}
 
-    # trigger a config_changed with a modified SAN
     with _sans_patch():
-        with ctx.manager("config_changed", state_out) as mgr:
+        with ctx.manager("update_status", state_out) as mgr:
             charm = mgr.charm
             state_out = mgr.run()
             csr = get_csr_obj(charm.ch._csr)
-            # assert CSR contains updated SAN
             assert get_sans_from_csr(csr) == {socket.getfqdn(), MOCK_HOSTNAME}
 
 
-def test_csr_no_change_on_wrong_refresh_event(ctx, certificates):
-    with _cert_renew_patch() as renew_patch:
-        with ctx.manager(
-            "config_changed",
-            State(leader=True, relations=[certificates]),
-        ) as mgr:
-            charm = mgr.charm
-            state_out = mgr.run()
-            orig_csr = get_csr_obj(charm.ch._csr)
-            assert get_sans_from_csr(orig_csr) == {socket.getfqdn()}
-
-    with _sans_patch():
-        with _cert_renew_patch() as renew_patch:
-            with ctx.manager("update_status", state_out) as mgr:
-                charm = mgr.charm
-                state_out = mgr.run()
-                csr = get_csr_obj(charm.ch._csr)
-                assert get_sans_from_csr(csr) == {socket.getfqdn()}
-                assert renew_patch.call_count == 0
-
-
 def test_csr_no_change(ctx, certificates):
 
     with ctx.manager(