Merge "Add deleted domain purging spec"

specs/liberty/deleted-domains-purging.rst

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+This work is licensed under a Creative Commons Attribution 3.0 Unported License.
+http://creativecommons.org/licenses/by/3.0/legalcode
+
+=============================
+ Deleted domains purging
+=============================
+
+https://blueprints.launchpad.net/designate/+spec/deleted-domains-purging
+
+Implementation of a mechanism to routinely purge deleted domains from the
+database.
+
+
+Problem description
+===================
+
+Once deleted, domains are not removed immediatly from the database, mostly for
+billing reasons. They are flagged as deleted in the "deleted" database column
+and the "deleted_at" column is populated with a timestamp.
+
+Currently, deleted domains are purged manually by running SQL queries against
+the database.
+The purging process impacts the database performance and requires manual
+intervention.
+
+Proposed change
+===============
+
+This change is to implement an automated purging mechanism for deleted domains.
+
+It also provides "purge_domain" and "purge_domains" calls to purge domains using an
+arbitrary criterion.
+
+
+API Changes
+-----------
+
+Central API bumps to version 5.3 with the addition of the "purge_domains" call.
+
+Zone Manager Changes
+--------------------
+
+Implement purging as a periodic task in Zone Manager using a "domain_purge"
+plugin. The task will select a group of domains and send a RPC call to Central.
+Central will run a query against the database to purge any deleted domain if
+needed and log the number of purged domains.
+
+Configuration paramenters:
+
+Purging run frequency.
+  Default: hourly. Users might want to run it frequently to minimize the cycle duration.
+
+Per-cycle purging limit.
+  Default: 100.
+
+Time threshold.
+  Default: 7 days.
+
+Configuration example:
+
+.. code-block:: cfg
+
+    # Deleted domains purging
+    #------------------------
+    [zone_manager:domain_purge]
+    # How frequently to purge deleted domains, in seconds
+    #run_interval = 3600  # 1h
+    # How many deleted domains to be purged on each run
+    #limit = 100
+    # How old deleted domains should be to be purged, in seconds (deleted_at column)
+    #time_threshold = 604800  # 7 days
+
+
+Central Changes
+---------------
+
+Implement purge_domains() method.
+
+Storage Changes
+---------------
+
+Implement purge_domain(), purge_domains() method.
+
+Update the _delete() method to allow forced hard delete.
+
+Other Changes
+-------------
+
+Add a new task to setup.cfg and a new purge_domains policy item to policy.json
+
+Add some test utility functions.
+
+Alternatives
+------------
+
+1) No change: keeping the current manual process in place.
+2) Deleting+purging the domains immediately.
+3) Purging the domains on a record creation/deletion event.
+4) Purging deleted domains with a single SQL query.
+
+Further improvements
+--------------------
+
+Domains for purging are queried with a column comparison "deleted_at > $date"
+
+Query performance can be improved by indexing the "deleted_at" column as a
+B-Tree (supported by InnoDB and MyISAM):
+https://dev.mysql.com/doc/refman/5.0/en/index-btree-hash.html
+
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  https://launchpad.net/~federico-ceratto
+
+Milestones
+----------
+
+Target Milestone for completion:
+  Libery-3
+
+Work Items
+----------
+
+* Implement purging
+* Update documentation
+* Implement benchmarks
+
+Dependencies
+============
+
+TODO