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diff --git a/doc/sphinx/Pacemaker_Development/evolution.rst b/doc/sphinx/Pacemaker_Development/evolution.rst new file mode 100644 index 0000000..31349c3 --- /dev/null +++ b/doc/sphinx/Pacemaker_Development/evolution.rst @@ -0,0 +1,90 @@ +Evolution of the project +------------------------ + +This section will not generally be of interest, but may occasionally +shed light on why the current code is structured the way it is when +investigating some thorny issue. + +Origin in Heartbeat project +########################### + +Pacemaker can be considered as a spin-off from Heartbeat, the original +comprehensive high availability suite started by Alan Robertson. Some +portions of code are shared, at least on the conceptual level if not verbatim, +till today, even if the effective percentage continually declines. + +Before Pacemaker 2.0, Pacemaker supported Heartbeat as a cluster layer +alternative to Corosync. That support was dropped for the 2.0.0 release (see +`commit 55ab749bf +<https://github.com/ClusterLabs/pacemaker/commit/55ab749bf0f0143bd1cd050c1bbe302aecb3898e>`_). + +An archive of a 2016 checkout of the Heartbeat code base is shared as a +`read-only repository <https://gitlab.com/poki/archived-heartbeat>`_. Notable +commits include: + +* `creation of Heartbeat's "new cluster resource manager," which evolved into + Pacemaker + <https://gitlab.com/poki/archived-heartbeat/commit/bb48551be418291c46980511aa31c7c2df3a85e4>`_ + +* `deletion of the new CRM from Heartbeat after Pacemaker had been split off + <https://gitlab.com/poki/archived-heartbeat/commit/74573ac6182785820d765ec76c5d70086381931a>`_ + +Regarding Pacemaker's split from heartbeat, it evolved stepwise (as opposed to +one-off cut), and the last step of full dependency is depicted in +`The Corosync Cluster Engine +<https://www.kernel.org/doc/ols/2008/ols2008v1-pages-85-100.pdf#page=14>`_ +paper, fig. 10. This article also provides a good reference regarding wider +historical context of the tangentially (and deeper in some cases) meeting +components around that time. + + +Influence of Heartbeat on Pacemaker +___________________________________ + +On a closer look, we can identify these things in common: + +* extensive use of data types and functions of + `GLib <https://wiki.gnome.org/Projects/GLib>`_ + +* Cluster Testing System (CTS), inherited from initial implementation + by Alan Robertson + +* ... + + +Notable Restructuring Steps in the Codebase +########################################### + +File renames may not appear as notable ... unless one runs into complicated +``git blame`` and ``git log`` scenarios, so some more massive ones may be +stated as well. + +* watchdog/'sbd' functionality spin-off: + + * `start separating, eb7cce2a1 + <https://github.com/ClusterLabs/pacemaker/commit/eb7cce2a172a026336f4ba6c441dedce42f41092>`_ + * `finish separating, 5884db780 + <https://github.com/ClusterLabs/pacemaker/commit/5884db78080941cdc4e77499bc76677676729484>`_ + +* daemons' rename for 2.0 (in chronological order) + + * `start of moving daemon sources from their top-level directories under new + /daemons hierarchy, 318a2e003 + <https://github.com/ClusterLabs/pacemaker/commit/318a2e003d2369caf10a450fe7a7616eb7ffb264>`_ + * `attrd -> pacemaker-attrd, 01563cf26 + <https://github.com/ClusterLabs/pacemaker/commit/01563cf2637040e9d725b777f0c42efa8ab075c7>`_ + * `lrmd -> pacemaker-execd, 36a00e237 + <https://github.com/ClusterLabs/pacemaker/commit/36a00e2376fd50d52c2ccc49483e235a974b161c>`_ + * `pacemaker_remoted -> pacemaker-remoted, e4f4a0d64 + <https://github.com/ClusterLabs/pacemaker/commit/e4f4a0d64c8b6bbc4961810f2a41383f52eaa116>`_ + * `crmd -> pacemaker-controld, db5536e40 + <https://github.com/ClusterLabs/pacemaker/commit/db5536e40c77cdfdf1011b837f18e4ad9df45442>`_ + * `pengine -> pacemaker-schedulerd, e2fdc2bac + <https://github.com/ClusterLabs/pacemaker/commit/e2fdc2baccc3ae07652aac622a83f317597608cd>`_ + * `stonithd -> pacemaker-fenced, 038c465e2 + <https://github.com/ClusterLabs/pacemaker/commit/038c465e2380c5349fb30ea96c8a7eb6184452e0>`_ + * `cib daemon -> pacemaker-based, 50584c234 + <https://github.com/ClusterLabs/pacemaker/commit/50584c234e48cd8b99d355ca9349b0dfb9503987>`_ + +.. TBD: + - standalone tengine -> part of crmd/pacemaker-controld |