Changes between Initial Version and Version 1 of Development/Features/PrePostActionsNCMNCD

Timestamp:

Jul 31, 2013, 7:14:30 PM (12 years ago)

Author:

munoz

Comment:

--

Development/Features/PrePostActionsNCMNCD

@@ +1 @@
+= Pre and post-configuration hooks on ncm-ncd =
+
+[[TracNav]]
+
+[[TOC(inline)]]
+
+== Introduction ==
+
+We want to be able to take actions before and after components are executed, with no link to the profile.  Use cases include:
+
+* Report the execution results to the monitoring right away.
+* Freezing and unfreezing services in the members of an HA setup.
+
+Users should be able to specify the actions that need to be taken.  However, these actions will not receive any `$config`-like object, or any profile representation.
+
+This came a long time ago, as part of our feedback during our LISA presentation.
+
+=== When hooks will run ===
+
+We'll run hooks as part of the `--configure` process only. We'll run them:
+
+* Before any components run (`run-init`).
+* After all components have run (`run-finalize`)
+
+We may discuss also:
+
+* Before the execution of each component.
+* After the execution of each component.
+
+But I'll implement these only if they are '''really''' needed.
+
+== Implementation ==
+
+=== Hook API ===
+
+==== run-init ====
+
+The pre-run action will receive no arguments. If it fails, it shall abort the execution of any configuration modules.
+
+==== run-finalize ====
+
+The post-run will receive the execution status (`%global_status` variable in [https://github.com/quattor/ncm-ncd/blob/master/src/main/perl/ComponentProxyList.pm#L87 NCD::ComponentProxyList::executeConfigComponents]) as its only argument.  If it fails, `ncm-ncd` will exit with a special exit code.
+
+=== Specifying the hooks ===
+
+We'll specify hooks in `/etc/ncm-ncd.conf`.  They will look like this:
+
+{{{
+#!ini
+run-init-hook = <hook-name>
+run-finalize-hook = <hook-name>
+}}}
+
+=== What a hook actually is ===
+
+We have two options here.  And I'll implement only one of them, what's the feeling of the community?
+
+==== Option 1: Perl module ====
+
+A Perl module inside, say, `NCD::Hooks` namespace.  It provides `run_init` and `run_finalize` methods.
+
+==== Option 2: an executable ====
+
+Perl is not the favourite language of many contributors, and they prefer to be able to write their hooks in a different language.  Any scripted hook that requires arguments would receive them as a JSON object via STDIN.