Merge ~vultaire/charm-nagios:allow-multiple-relation-data-sets-per-host into charm-nagios:master

[Paul Goins]

Keep writing config for newly-created config files

With the new logic, we try to write only the files we need to.
However, there may legitimately be cases where there's multiple sets
of data associated with the same host name (e.g. multiple nrpe units),
and at present, only the first set of such data will actually be
written.

This change tracks files which are being newly created, and will allow
multiple sets of relation data to be written to the same file, if
necessary.

[🤖 prod-jenkaas-bootstack (prod-jenkaas-bootstack)]

A CI job is currently in progress. A follow up comment will be added when it completes.

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Paul Goins (vultaire)]

Note: I did replace some items/iteritems calls with itervalues as a cleanup to remove unused vars.

[🤖 prod-jenkaas-bootstack (prod-jenkaas-bootstack)]

FAILED: Continuous integration, rev:525739b24923babdde61f66b5caf292340c1181b
https://jenkins.canonical.com/bootstack/job/lp-charm-nagios-ci/29/
Executed test runs:
    FAILURE: https://jenkins.canonical.com/bootstack/job/lp-charm-test-functest/99/
    None: https://jenkins.canonical.com/bootstack/job/lp-update-mp/470/

Click here to trigger a rebuild:
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review: Needs Fixing (continuous-integration)

[🤖 prod-jenkaas-bootstack (prod-jenkaas-bootstack)]

FAILED: Continuous integration, rev:525739b24923babdde61f66b5caf292340c1181b
https://jenkins.canonical.com/bootstack/job/lp-charm-nagios-ci/30/
Executed test runs:
    FAILURE: https://jenkins.canonical.com/bootstack/job/lp-charm-test-functest/102/
    None: https://jenkins.canonical.com/bootstack/job/lp-update-mp/473/

Click here to trigger a rebuild:
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review: Needs Fixing (continuous-integration)

[🤖 prod-jenkaas-bootstack (prod-jenkaas-bootstack)]

PASSED: Continuous integration, rev:525739b24923babdde61f66b5caf292340c1181b
https://jenkins.canonical.com/bootstack/job/lp-charm-nagios-ci/31/
Executed test runs:
    SUCCESS: https://jenkins.canonical.com/bootstack/job/lp-charm-test-functest/104/
    None: https://jenkins.canonical.com/bootstack/job/lp-update-mp/475/

Click here to trigger a rebuild:
https://jenkins.canonical.com/bootstack/job/lp-charm-nagios-ci/31//rebuild

review: Approve (continuous-integration)

[Xav Paice (xavpaice)]

LGTM

review: Approve

[Garrett Neugent (thogarre)]

LGTM

review: Approve

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision 054394442a902a178477b9855a4e06d1aa974bea

diff --git a/hooks/monitors_relation_changed.py b/hooks/monitors_relation_changed.py
index 4c86a63..b24ed5c 100755
--- a/hooks/monitors_relation_changed.py
+++ b/hooks/monitors_relation_changed.py
@@ -199,8 +199,9 @@ def main(argv, full_rewrite=False):  # noqa: C901
     else:
         status_set("active", "ready")
 
-    for relid, units in all_relations.items():
-        apply_relation_config(relid, units, all_hosts)
+    new_file_set = set()
+    for units in all_relations.itervalues():
+        apply_relation_config(units, all_hosts, new_file_set)
 
     cleanup_leftover_hosts(all_relations)
     refresh_hostgroups()
@@ -261,13 +262,15 @@ def compute_host_prefixes(model_ids):
     return result
 
 
-def apply_relation_config(relid, units, all_hosts):  # noqa: C901
-    for unit, relation_settings in units.iteritems():
+def apply_relation_config(units, all_hosts, new_file_set):  # noqa: C901
+    for relation_settings in units.itervalues():
         target_id = relation_settings[TARGET_ID_KEY]
-        if os.path.exists(get_nagios_host_config_path(target_id)):
+        host_config_path = get_nagios_host_config_path(target_id)
+        if os.path.exists(host_config_path) and host_config_path not in new_file_set:
             # Skip updating files unrelated to the hook at hand unless they were
             # deliberately removed with the intent of them being rewritten.
             continue
+        new_file_set.add(host_config_path)
 
         monitors = relation_settings["monitors"]
         machine_id = relation_settings.get(MACHINE_ID_KEY)