OpenStack Storage (Swift)
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Clay Gerrard 18cdf9b568 Populate shrinking shards with shard ranges learnt from root
Shard shrinking can be instigated by a third party modifying shard
ranges, moving one shard to shrinking state and expanding the
namespace of one or more other shard(s) to act as acceptors. These
state and namespace changes must propagate to the shrinking and
acceptor shards. The shrinking shard must also discover the acceptor
shard(s) into which it will shard itself.

The sharder audit function already updates shards with their own state
and namespace changes from the root. However, there is currently no
mechanism for the shrinking shard to learn about the acceptor(s) other
than by a PUT request being made to the shrinking shard container.

This patch modifies the shard container audit function so that other
overlapping shards discovered from the root are merged into the
audited shard's db. In this way, the audited shard will have acceptor
shards to cleave to if shrinking.

This new behavior is restricted to when the shard is shrinking. In
general, a shard is responsible for processing its own sub-shard
ranges (if any) and reporting them to root. Replicas of a shard
container synchronise their sub-shard ranges via replication, and do
not rely on the root to propagate sub-shard ranges between shard
replicas. The exception to this is when a third party (or
auto-sharding) wishes to instigate shrinking by modifying the shard
and other acceptor shards in the root container.  In other
circumstances, merging overlapping shard ranges discovered from the
root is undesirable because it risks shards inheriting other unrelated
shard ranges. For example, if the root has become polluted by
split-brain shard range management, a sharding shard may have its
sub-shards polluted by an undesired shard from the root.

During the shrinking process a shard range's own shard range state may
be either shrinking or, prior to this patch, sharded. The sharded
state could occur when one replica of a shrinking shard completed
shrinking and moved the own shard range state to sharded before other
replica(s) had completed shrinking. This makes it impossible to
distinguish a shrinking shard (with sharded state), which we do want
to inherit shard ranges, from a sharding shard (with sharded state),
which we do not want to inherit shard ranges.

This patch therefore introduces a new shard range state, 'SHRUNK', and
applies this state to shard ranges that have completed shrinking.
Shards are now restricted to inherit shard ranges from the root only
when their own shard range state is either SHRINKING or SHRUNK.

This patch also:

 - Stops overlapping shrinking shards from generating audit warnings:
   overlaps are cured by shrinking and we therefore expect shrinking
   shards to sometimes overlap.

 - Extends an existing probe test to verify that overlapping shard
   ranges may be resolved by shrinking a subset of the shard ranges.

 - Adds a --no-auto-shard option to swift-container-sharder to enable the
   probe tests to disable auto-sharding.

 - Improves sharder logging, in particular by decrementing ranges_todo
   when a shrinking shard is skipped during cleaving.

 - Adds a ShardRange.sort_key class method to provide a single definition
   of ShardRange sort ordering.

 - Improves unit test coverage for sharder shard auditing.

Co-Authored-By: Tim Burke <tim.burke@gmail.com>
Co-Authored-By: Alistair Coles <alistairncoles@gmail.com>
Cherry-Picked-From: I9034a5715406b310c7282f1bec9625fe7acd57b6
Change-Id: Ifc5d1ae142f63520df49fe610c94b332dcea3180
2021-02-23 20:47:35 -06:00
api-ref/source Update hacking for Python3 2020-04-03 21:21:07 +02:00
bin Populate shrinking shards with shard ranges learnt from root 2021-02-23 20:47:35 -06:00
doc Merge "docs: Encourage usage of UUID inside /etc/fstab in examples" 2020-04-04 22:48:30 +00:00
docker Merge "Add etag quoter to saio proxy config" 2020-03-26 00:51:18 +00:00
etc Memcached client TLS support 2021-01-07 22:05:42 +01:00
examples display swift services in apache2 2017-03-07 19:23:15 +00:00
releasenotes Authors/ChangeLog for 2.25.1 2020-10-05 15:19:11 -07:00
swift Populate shrinking shards with shard ranges learnt from root 2021-02-23 20:47:35 -06:00
test Populate shrinking shards with shard ranges learnt from root 2021-02-23 20:47:35 -06:00
tools Merge "Give probe tests a second chance to pass" into stable/ussuri 2021-02-22 06:18:01 +00:00
.alltests tests: Stop invoking python just to get the real source directory 2019-10-15 15:08:42 -07:00
.coveragerc Show missing branches in coverage report. 2017-12-14 14:57:48 -08:00
.dockerignore Add Dockerfile to build a SAIO container image 2019-05-07 15:44:00 -04:00
.functests tests: Stop invoking python just to get the real source directory 2019-10-15 15:08:42 -07:00
.gitignore Give unit tests a second chance to pass 2021-02-11 21:32:02 +00:00
.gitreview Update .gitreview for stable/ussuri 2020-04-20 09:59:55 +00:00
.mailmap Authors/ChangeLog for 2.25.0 2020-04-17 17:12:48 -07:00
.manpages Script for checking sanity of manpages 2016-02-10 14:16:56 -08:00
.probetests tests: Stop invoking python just to get the real source directory 2019-10-15 15:08:42 -07:00
.testr.conf Fix func test --until-failure and --no-discover options 2015-12-16 15:28:25 +00:00
.unittests tests: Stop invoking python just to get the real source directory 2019-10-15 15:08:42 -07:00
.zuul.yaml Give probe tests a second chance to pass 2021-02-11 13:45:40 -08:00
AUTHORS Authors/ChangeLog for 2.25.1 2020-10-05 15:19:11 -07:00
CHANGELOG Authors/ChangeLog for 2.25.1 2020-10-05 15:19:11 -07:00
CONTRIBUTING.rst Replace git.openstack.org URLs with opendev.org URLs 2019-04-24 09:56:54 +08:00
Dockerfile Add Dockerfile to build a py3 swift docker image 2019-08-19 22:31:41 +02:00
Dockerfile-py3 Add Dockerfile to build a py3 swift docker image 2019-08-19 22:31:41 +02:00
LICENSE Convert LICENSE to use unix style line endings. 2012-12-19 12:48:27 -05:00
MANIFEST.in Include s3api schemas in sdists 2018-07-11 16:56:28 -07:00
README.rst Start README.rst with a better title 2019-11-19 17:32:50 +01:00
REVIEW_GUIDELINES.rst Fix the duplicated words issue like "the the " 2020-01-06 10:34:42 +08:00
babel.cfg add pybabel setup.py commands and initial .pot 2011-01-27 00:01:24 +00:00
bandit.yaml Update the bandit.yaml available tests list 2019-07-30 13:46:01 +08:00
bindep.txt Require gettext for all non-SUSE distros 2018-10-22 18:06:00 +00:00
lower-constraints.txt Update hacking for Python3 2020-04-03 21:21:07 +02:00
requirements.txt Give ECAppIter greenthreads a chance to wrap up 2019-07-29 12:11:34 -07:00
setup.cfg Middleware that allows a user to have quoted Etags 2020-01-27 12:53:35 -08:00
setup.py taking the global reqs that we can 2014-05-21 09:37:22 -07:00
test-requirements.txt [stable-only] Cap bandit to 1.6.2 2021-01-05 15:39:48 -08:00
tox.ini Give unit tests a second chance to pass 2021-02-11 21:32:02 +00:00

README.rst

OpenStack Swift

image

OpenStack Swift is a distributed object storage system designed to scale from a single machine to thousands of servers. Swift is optimized for multi-tenancy and high concurrency. Swift is ideal for backups, web and mobile content, and any other unstructured data that can grow without bound.

Swift provides a simple, REST-based API fully documented at https://docs.openstack.org/swift/latest/.

Swift was originally developed as the basis for Rackspace's Cloud Files and was open-sourced in 2010 as part of the OpenStack project. It has since grown to include contributions from many companies and has spawned a thriving ecosystem of 3rd party tools. Swift's contributors are listed in the AUTHORS file.

Docs

To build documentation run:

pip install -r requirements.txt -r doc/requirements.txt
sphinx-build -W -b html doc/source doc/build/html

and then browse to doc/build/html/index.html. These docs are auto-generated after every commit and available online at https://docs.openstack.org/swift/latest/.

For Developers

Getting Started

Swift is part of OpenStack and follows the code contribution, review, and testing processes common to all OpenStack projects.

If you would like to start contributing, check out these notes to help you get started.

The best place to get started is the "SAIO - Swift All In One". This document will walk you through setting up a development cluster of Swift in a VM. The SAIO environment is ideal for running small-scale tests against Swift and trying out new features and bug fixes.

Tests

There are three types of tests included in Swift's source tree.

  1. Unit tests
  2. Functional tests
  3. Probe tests

Unit tests check that small sections of the code behave properly. For example, a unit test may test a single function to ensure that various input gives the expected output. This validates that the code is correct and regressions are not introduced.

Functional tests check that the client API is working as expected. These can be run against any endpoint claiming to support the Swift API (although some tests require multiple accounts with different privilege levels). These are "black box" tests that ensure that client apps written against Swift will continue to work.

Probe tests are "white box" tests that validate the internal workings of a Swift cluster. They are written to work against the "SAIO - Swift All In One" dev environment. For example, a probe test may create an object, delete one replica, and ensure that the background consistency processes find and correct the error.

You can run unit tests with .unittests, functional tests with .functests, and probe tests with .probetests. There is an additional .alltests script that wraps the other three.

To fully run the tests, the target environment must use a filesystem that supports large xattrs. XFS is strongly recommended. For unit tests and in-process functional tests, either mount /tmp with XFS or provide another XFS filesystem via the TMPDIR environment variable. Without this setting, tests should still pass, but a very large number will be skipped.

Code Organization

  • bin/: Executable scripts that are the processes run by the deployer
  • doc/: Documentation
  • etc/: Sample config files
  • examples/: Config snippets used in the docs
  • swift/: Core code
    • account/: account server
    • cli/: code that backs some of the CLI tools in bin/
    • common/: code shared by different modules
      • middleware/: "standard", officially-supported middleware
      • ring/: code implementing Swift's ring
    • container/: container server
    • locale/: internationalization (translation) data
    • obj/: object server
    • proxy/: proxy server
  • test/: Unit, functional, and probe tests

Data Flow

Swift is a WSGI application and uses eventlet's WSGI server. After the processes are running, the entry point for new requests is the Application class in swift/proxy/server.py. From there, a controller is chosen, and the request is processed. The proxy may choose to forward the request to a back-end server. For example, the entry point for requests to the object server is the ObjectController class in swift/obj/server.py.

For Deployers

Deployer docs are also available at https://docs.openstack.org/swift/latest/. A good starting point is at https://docs.openstack.org/swift/latest/deployment_guide.html There is an ops runbook that gives information about how to diagnose and troubleshoot common issues when running a Swift cluster.

You can run functional tests against a Swift cluster with .functests. These functional tests require /etc/swift/test.conf to run. A sample config file can be found in this source tree in test/sample.conf.

For Client Apps

For client applications, official Python language bindings are provided at https://github.com/openstack/python-swiftclient.

Complete API documentation at https://docs.openstack.org/api-ref/object-store/

There is a large ecosystem of applications and libraries that support and work with OpenStack Swift. Several are listed on the associated projects page.


For more information come hang out in #openstack-swift on freenode.

Thanks,

The Swift Development Team