Merge ~prometheus-charmers/charm-prometheus2:core-resource into ~prometheus-charmers/charm-prometheus2:master

[Kevin W Monroe]

lp:1828063 add a core.snap resource to facilitate offline installs

The core snap is required by the prometheus snap. To facilitate offline deployment, users need the ability to attach a core.snap resource in addition to the prometheus.snap resource.

A downside of this is that future prometheus2 charm releases will need to have a zero-byte core.snap resource attached, as in:

rm /tmp/core.snap && touch /tmp/core.snap
charm push /path/to/prometheus2-charm --resource core=/tmp/core.snap
charm release <prometheus2-X> --resource core-0 --resource prometheus-Y

For normal deployments, layer-snap will recognize that core.snap is a 0-byte resource and will fall back to installing from the snap store. For offline deployments, users will need to attach the desired core.snap, as in:

juju deploy /path/to/prometheus2-charm \
  --resource core=/path/to/real/core.snap \
  --resource prometheus=/path/to/real/prometheus.snap

Also in offline deployments, we need to ensure the core.snap is installed prior to prometheus.snap, hence this is dependent on:

https://github.com/stub42/layer-snap/pull/22.

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

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

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

Unable to determine commit message from repository - please click "Set commit message" and enter the commit message manually.

[George Kraft (cynerva)]

LGTM

> Also in offline deployments, we need to ensure the core.snap is installed prior to prometheus.snap, hence this is dependent on: https://github.com/stub42/layer-snap/pull/22.

I don't think that layer-snap PR is a dependency for this, since it only applies to charms that use the layer.yaml snap options.

[Stuart Bishop (stub)]

Looks good.

I would like to request a brief developer's readme/howto or at least a Makefile rule which details how to build and publish the snap, while you are here making this more complex than it already is.

The snap layer PR has been merged and released.

review: Approve

[Kevin W Monroe (kwmonroe)]

@stub, I added a makefile target with some helpful text for developers:

$ make charmrelease
---------------------------------------------------------------------
prometheus2 supports core and prometheus snap resources.

Attached resources will be processed during charm deployment. If a
zero-byte resource is found, the charm will install the relevant snap
from the store. This provides flexibility in choosing which snaps will
be installed by the charm.

For example, release a charm that uses the core snap from the store
(0-byte resource attached) along with a specific prometheus snap:

cd /tmp
rm empty-core.snap && touch empty-core.snap
snap download --channel=2/stable prometheus
charm push /Users/kwmonroe/charms/builds/prometheus2 --resource core=/tmp/empty-core.snap --resource prometheus=/tmp/prometheus_*.snap
charm release <revision> --resource core-<m> --resource prometheus-<n>

If the resources you want already exist in the charm store, omit the
declarations during 'charm push' and specify resource revisions
during 'charm release':

charm push /Users/kwmonroe/charms/builds/prometheus2
charm release <revision> --resource core-0 --resource prometheus-0
---------------------------------------------------------------------

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

Change successfully merged at revision 89dc19ff15b5b7dfcd268c2027e0ff7e0530d607

diff --git a/Makefile b/Makefile
index 76b37de..ab0dbb3 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,45 @@
+BUILDDEST:=$(if $(JUJU_REPOSITORY),$(JUJU_REPOSITORY),"../prometheus2-built")
+BUILTCHARMDIR:="$(BUILDDEST)/builds/prometheus2"
+
+.PHONY: charmbuild
+charmbuild:
+	charm build --output-dir $(BUILDDEST) --report --no-local-layers
+
+.PHONY: charmrelease
+charmrelease:
+	@echo ---------------------------------------------------------------------
+	@echo prometheus2 supports 'core' and 'prometheus' snap resources.
+	@echo
+	@echo Attached resources will be processed during charm deployment. If a
+	@echo zero-byte resource is found, the charm will install the relevant snap
+	@echo from the store. This provides flexibility in choosing which snaps will
+	@echo be installed by the charm.
+	@echo
+	@echo For example, release a charm that uses the core snap from the store
+	@echo \(0-byte resource attached\) along with a specific prometheus snap:
+	@echo
+	@echo cd /tmp
+	@echo rm empty-core.snap \&\& touch empty-core.snap
+	@echo snap download --channel=2/stable prometheus
+	@echo charm push $(BUILTCHARMDIR) --resource core=/tmp/empty-core.snap --resource prometheus=/tmp/prometheus_*.snap
+	@echo charm release \<revision\> --resource core-\<m\> --resource prometheus-\<n\>
+	@echo
+	@echo If the resources you want already exist in the charm store, omit the
+	@echo declarations during \'charm push\' and specify resource revisions
+	@echo during \'charm release\':
+	@echo
+	@echo charm push $(BUILTCHARMDIR)
+	@echo charm release \<revision\> --resource core-0 --resource prometheus-0
+	@echo ---------------------------------------------------------------------
+
+.PHONY: clean
+clean:
+	@echo "Cleaning files"
+	@rm -f .coverage .unit-state.db
+	@find . -name "*.pyc" -type f -exec rm -f '{}' \;
+	@find . -name "__pycache__" -type d -prune -exec rm -rf '{}' \;
+	@rm -rf ./.tox
+
 .PHONY: test
 test: unittest
 
diff --git a/README.md b/README.md
index f9bfa85..0581e89 100644
--- a/README.md
+++ b/README.md
@@ -41,10 +41,11 @@ For example to deploy with local filesystem run:
 
 ## Juju resources support
 
-The charm support juju resources, which is handy in offline deployments. Prefetch the snap:
+The charm support juju resources, which is handy in offline deployments. Prefetch the snaps:
 
+    snap download --channel=stable core
     snap download --channel=2/stable prometheus
 
-Provide downloaded snap (prometheus_20.snap) as a resource to the application:
+Provide downloaded snaps as resources to the application:
 
-    juju deploy cs:prometheus2 --resource prometheus=prometheus_20.snap
+    juju deploy cs:prometheus2 --resource core=core_6818.snap --resource prometheus=prometheus_20.snap
diff --git a/metadata.yaml b/metadata.yaml
index bc054ac..7b72d5c 100644
--- a/metadata.yaml
+++ b/metadata.yaml
@@ -36,6 +36,10 @@ requires:
   prometheus-rules:
     interface: prometheus-rules
 resources:
+  core:
+    type: file
+    filename: core.snap
+    description: Snap package of core
   prometheus:
     type: file
     filename: prometheus.snap
diff --git a/reactive/prometheus.py b/reactive/prometheus.py
index 32796b7..e06bdc0 100644
--- a/reactive/prometheus.py
+++ b/reactive/prometheus.py
@@ -198,6 +198,7 @@ def install_packages():
 
     if not os.path.exists('/usr/sbin/sendmail'):
         fetch.apt_install('sendmail-bin')  # Needed for cronjob email notifications
+    snap.install('core')  # Needed for offline deploy; falls back to store as needed
     snap.install(pkgname, channel=channel, force_dangerous=False)
     if config.get('prometheus_registration_listen', False):
         channel = config.get('promreg_snap_channel', 'stable')