Merge bootstack-ops:add-snapcraft-base into bootstack-ops:master

[James Hebden]

Moved to using snapcraft bases and updated for snapcraft 3.0

Snapcraft 3.0 introduces the concept of bases, which allows the building of snaps on multipass-based core images, to prevent dependency hell, and streamline the build process.

This merge adds the core snap as a base, which is the 16.04 core snap. In the future, we should move to core18, however the dependency on the 9.5 postgresql client requires more thought for this to happen. As such, I've used the core snap instead of core18.

Snapcraft 3.0 also removes the 'install' property for running a script during the snap build, which we use to update the alternative for pg_dumpall to point to postgresql 9.5. The way to accomplish the same thing is to use the build-override setting, which is also included in this merge for the purpose of ensuring Snapcraft 3.0 compatibility.

Also updated the README.md with build instructions.

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

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

[David O Neill (dmzoneill)]

review: Approve

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

Change successfully merged at revision 8000536ab90b4abb8a3368acc651578c98f079a5

diff --git a/README.md b/README.md
index 58a14d0..b958108 100644
--- a/README.md
+++ b/README.md
@@ -55,3 +55,13 @@ echo "0 4 * * * jujumanage PATH=\${PATH}:/snap/bin bootstack-ops.backup --cloud-
 
 Note for both these, we export JUJU_DATA - this is so that we can use the
 existing configured Juju client rather than having to configure our own.
+
+### Building the snap ###
+
+This snap makes use of the snapcraft 3.0 bases functionality to automatically configure a compatible build environment and base core snap.
+It uses the core18 (Bionic) base snap. By default, building this snap will use multipass to install a compatible build environment and automatically use this to build the
+snap. This prevents dependency issues when building on newer versions of Ubuntu, which may have newer standard libraries that the core snap upon which snaps run.
+
+To build the snap and all dependencies on a supported version of core, using multipass, simply run: `snapcraft`
+
+This will build the snap to a .snap file which you can deploy with --devmode. This snap is not yet published to the store.
diff --git a/snap/snapcraft.yaml b/snap/snapcraft.yaml
index 5b36ff4..e1ebf50 100644
--- a/snap/snapcraft.yaml
+++ b/snap/snapcraft.yaml
@@ -1,5 +1,6 @@
 name: bootstack-ops
 version: '0.3' # just for humans, typically '1.2+git' or '1.3.2'
+base: core
 summary: Bootstack tooling for Bootstack clouds
 description: |
   BootStack is a managed service where the world-class team at Canonical build
@@ -52,15 +53,17 @@ apps:
 parts:
   bootstack-ops:
     plugin: python
-    requirements: requirements.txt
+    override-build: |
+      snapcraftctl build
+      rm $SNAPCRAFT_PART_INSTALL/usr/bin/pg_dumpall
+      ln -s ../lib/postgresql/9.5/bin/pg_dumpall $SNAPCRAFT_PART_INSTALL/usr/bin/pg_dumpall
+    requirements:
+      - requirements.txt
     source: ./
     stage-packages:
       - libc6
       - postgresql-client-9.5
       - locales
       - rsync
-    install: |
-      rm $SNAPCRAFT_PART_INSTALL/usr/bin/pg_dumpall
-      ln -s ../lib/postgresql/9.5/bin/pg_dumpall $SNAPCRAFT_PART_INSTALL/usr/bin/pg_dumpall