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========
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Upgrades
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========
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@@ -11,6 +12,7 @@ Keeping the control plane running during an upgrade is more difficult. This
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document's goal is to provide preliminaries and a detailed procedure of such
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upgrade.
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Concepts
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--------
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@@ -18,7 +20,7 @@ Here are the key concepts you need to know before reading the section on the
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upgrade process:
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RPC version pinning
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'''''''''''''''''''
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~~~~~~~~~~~~~~~~~~~
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Through careful RPC versioning, newer services are able to talk to older
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services (and vice-versa). The versions are autodetected using information
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@@ -27,7 +29,7 @@ or ``ServiceTooOld`` exceptions on service start, you're probably having some
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old orphaned records in that table.
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Graceful service shutdown
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'''''''''''''''''''''''''
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~~~~~~~~~~~~~~~~~~~~~~~~~
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Many cinder services are python processes listening for messages on an AMQP
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queue. When the operator sends SIGTERM signal to the process, it stops getting
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@@ -37,35 +39,51 @@ process starts back up. This gives us a way to shutdown a service using older
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code, and start up a service using newer code with minimal impact.
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.. note::
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Waiting for completion of long-running operations (e.g. slow volume copy
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operation) may take a while.
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.. note::
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This was tested with RabbitMQ messaging backend and may vary with other
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backends.
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Online Data Migrations
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''''''''''''''''''''''
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Database upgrades
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~~~~~~~~~~~~~~~~~
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To make DB schema migrations less painful to execute, since Liberty, all data
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migrations are banned from schema migration scripts. Instead, the migrations
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should be done by background process in a manner that doesn't interrupt running
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services (you can also execute online data migrations with services turned off
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if you're doing a cold upgrade). In Ocata a new ``cinder-manage db
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online_data_migrations`` utility was added for that purpose. Before upgrading
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Ocata to Pike, you need to run this tool in the background, until it tells you
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no more migrations are needed. Note that you won't be able to apply Pike's
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schema migrations before completing Ocata's online data migrations.
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Cinder has two types of database upgrades in use:
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- Schema migrations
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- Data migrations
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Schema migrations are defined in ``cinder/db/migrations/versions``. They are
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the routines that transform our database structure, which should be additive
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and able to be applied to a running system before service code has been
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upgraded.
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Data migrations are banned from schema migration scripts and are instead
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defined in ``cinder/db/api.py``. They are kept separate to make DB schema
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migrations less painful to execute. Instead, the migrations are executed by a
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background process in a manner that doesn't interrupt running services (you can
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also execute online data migrations with services turned off if you're doing a
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cold upgrade). The ``cinder-manage db online_data_migrations`` utility can be
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used for this purpose. Before upgrading N to N+1, you need to run this tool in
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the background until it tells you no more migrations are needed. Note that you
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won't be able to apply N+1's schema migrations before completing N's online
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data migrations.
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For information on developing your own schema migrations as part of a feature
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or bugfix, refer to **TODO**.
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API load balancer draining
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''''''''''''''''''''''''''
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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When upgrading API nodes, you can make your load balancer only send new
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connections to the newer API nodes, allowing for a seamless update of your API
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nodes.
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DB prune deleted rows
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'''''''''''''''''''''
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~~~~~~~~~~~~~~~~~~~~~
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Currently resources are soft deleted in the database, so users are able to
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track instances in the DB that are created and destroyed in production.
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@@ -77,18 +95,19 @@ longer as there is more data to migrate. To make pruning easier there's a
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records older than specified age.
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Versioned object backports
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''''''''''''''''''''''''''
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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RPC pinning ensures new services can talk to the older service's method
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signatures. But many of the parameters are objects that may well be too new for
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the old service to understand. Cinder makes sure to backport an object to a
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version that it is pinned to before sending.
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Minimal Downtime Upgrade Procedure
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----------------------------------
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Plan your upgrade
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'''''''''''''''''
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~~~~~~~~~~~~~~~~~
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* Read and ensure you understand the release notes for the next release.
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@@ -96,32 +115,33 @@ Plan your upgrade
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database. Hence, in case of upgrade failure, restoring database from backup
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is the only choice.
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* Note that there's an assumption that live upgrade can be performed only
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between subsequent releases. This means that you cannot upgrade Liberty
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directly into Newton, you need to upgrade to Mitaka first.
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* To avoid dependency hell it is advised to have your Cinder services deployed
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separately in containers or Python venvs.
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* Note that Cinder is basing version detection on what is reported in the
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``services`` table in the DB. Before upgrade make sure you don't have any
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orphaned old records there, because these can block starting newer services.
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You can clean them up using ``cinder-manage service remove <binary> <host>``
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.. note::
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Cinder is basing version detection on what is reported in the ``services``
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table in the DB. Before upgrade make sure you don't have any orphaned old
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records there, because these can block starting newer services. You can
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clean them up using ``cinder-manage service remove <binary> <host>``
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command.
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* Assumed service upgrade order is cinder-scheduler, cinder-volume,
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cinder-backup and finally cinder-api.
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Note that there's an assumption that live upgrade can be performed only between
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subsequent releases. This means that you cannot upgrade N directly to N+2, you
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need to upgrade to N+1 first.
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The assumed service upgrade order is ``cinder-scheduler``, ``cinder-volume``,
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``cinder-backup`` and finally ``cinder-api``.
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Rolling upgrade process
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'''''''''''''''''''''''
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~~~~~~~~~~~~~~~~~~~~~~~
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To reduce downtime, the services can be upgraded in a rolling fashion. It means
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upgrading a few services at a time. To minimise downtime you need to have HA
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Cinder deployment, so at the moment a service is upgraded, you'll keep other
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service instances running.
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Before maintenance window
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"""""""""""""""""""""""""
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.. rubric:: Before maintenance window
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* First you should execute required DB schema migrations. To achieve that
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without interrupting your existing installation, install new Cinder code in
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@@ -133,8 +153,7 @@ Before maintenance window
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DB schema changes are done in a way that both the N and N+1 release can
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perform operations against the same schema.
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During maintenance window
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"""""""""""""""""""""""""
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.. rubric:: During maintenance window
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1. The first service is cinder-scheduler. It is load-balanced by the message
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queue, so the only thing you need to worry about is to shut it down
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@@ -204,9 +223,7 @@ During maintenance window
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7. Then you should repeat step 6 for all of the cinder-api services.
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After maintenance window
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""""""""""""""""""""""""
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.. rubric:: After maintenance window
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* Once all services are running the new code, double check in the DB that
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there are no old orphaned records in ``services`` table (Cinder doesn't
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Stephen Finucane