Merge ~cjwatson/charm-postfix-relay:optional-myhostname into charm-postfix-relay:master

[Colin Watson]

Default myhostname to the system's FQDN

There isn't really a strong reason to require units to have an externally-resolvable hostname, especially for a subordinate charm. It's quite common for internet email to originate at a host that isn't even externally-routable never mind having an externally-resolvable hostname, and this is fine as long as it's relaying to something whose hostname can be resolved by the next hop in the chain.

A better default is to just let Postfix use the system's fully-qualified domain name from `gethostname`, which is its default. That way, this charm can be deployed on units that aren't exposed to the internet, and they can just be configured to relay to something that does have an externally-resolvable hostname.

(The prerequisite branch is simply due to the various CI fixes there.)

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

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

[Tianqi Xiao (txiao)]

The changes LGTM. I'm putting "Needs information" for now until the CI runs successfully.

review: Needs Information

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

FAILED: Continuous integration, rev:a5dc509cff9a9f1d49614883235caba9c7c9f829
https://jenkins.canonical.com/bootstack/job/lp-charm-postfix-relay-ci/5/
Executed test runs:
    FAILURE: https://jenkins.canonical.com/bootstack/job/lp-charm-test-functest/1094/
    None: https://jenkins.canonical.com/bootstack/job/lp-update-mp/1510/

Click here to trigger a rebuild:
https://jenkins.canonical.com/bootstack/job/lp-charm-postfix-relay-ci/5//rebuild

review: Needs Fixing (continuous-integration)

[Robert Gildein (rgildein)]

LGTM

review: Approve

[Eric Chen (eric-chen)]

mark it as WIP until the jenkins bot pass.

[Robert Gildein (rgildein)]

This can be rebased on current master and CI will work fine.

[Colin Watson (cjwatson)]

Rebased, thanks.

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

PASSED: Continuous integration, rev:8f371ca57c46e6c779da9f111a34e190267795ce
https://jenkins.canonical.com/bootstack/job/lp-charm-postfix-relay-ci/11/
Executed test runs:
    SUCCESS: https://jenkins.canonical.com/bootstack/job/lp-charm-test-functest/1148/
    None: https://jenkins.canonical.com/bootstack/job/lp-update-mp/1566/

Click here to trigger a rebuild:
https://jenkins.canonical.com/bootstack/job/lp-charm-postfix-relay-ci/11//rebuild

review: Approve (continuous-integration)

[Eric Chen (eric-chen)]

LGTM

review: Approve

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

Change successfully merged at revision 75a9c22abd684ff1f1f7dd01d4735ab6d9472fcd

diff --git a/src/config.yaml b/src/config.yaml
index ba05447..a28cf40 100644
--- a/src/config.yaml
+++ b/src/config.yaml
@@ -14,10 +14,10 @@ options:
             user+host@newdomain.
         type: string
     myhostname:
-        default: postfix-relay.example.com
+        default: ''
         description:
-            The external hostname by which this mail relay is known.  This
-            value must be changed for the charm to be useful.
+            The external hostname by which this mail relay is known.  If not
+            set, Postfix will default to using the system's FQDN.
         type: string
     mynetworks:
         default: 127.0.0.0/8
diff --git a/src/templates/main.cf b/src/templates/main.cf
index 32a8314..a1df893 100644
--- a/src/templates/main.cf
+++ b/src/templates/main.cf
@@ -23,7 +23,9 @@ smtp_sasl_security_options =
 {%- endif %}
 
 disable_vrfy_command = {{ disable_vrfy_command }}
+{%- if config.myhostname %}
 myhostname = {{ config.myhostname }}
+{%- endif %}
 mynetworks = {{ config.mynetworks }}
 mydestination = $myhostname, localhost.$mydomain, localhost
 relayhost = {{ config.relayhost }}