swift-ring-builder - Online in the Cloud

PROGRAM:

NAME

swift-ring-builder - Openstack-swift ring builder

SYNOPSIS

swift-ring-builder <builder_file> <commands> <arguments> <...>

DESCRIPTION

The swift-ring-builder utility is used to create, search and manipulate the swift storage
ring. The ring-builder assigns partitions to devices and writes an optimized Python
structure to a gzipped, pickled file on disk for shipping out to the servers. The server
processes just check the modification time of the file occasionally and reload their in-
memory copies of the ring structure as needed. Because of how the ring-builder manages
changes to the ring, using a slightly older ring usually just means one of the three
replicas for a subset of the partitions will be incorrect, which can be easily worked
around.

The ring-builder also keeps its own builder file with the ring information and additional
data required to build future rings. It is very important to keep multiple backup copies
of these builder files. One option is to copy the builder files out to every server while
copying the ring files themselves. Another is to upload the builder files into the
cluster itself. Complete loss of a builder file will mean creating a new ring from
scratch, nearly all partitions will end up assigned to different devices, and therefore
nearly all data stored will have to be replicated to new locations. So, recovery from a
builder file loss is possible, but data will definitely be unreachable for an extended
time.

If invoked as 'swift-ring-builder-safe' the directory containing the builder file provided
will be locked (via a .lock file in the files parent directory). This provides a basic
safe guard against multiple instances of the swift-ring-builder (or other utilities that
observe this lock) from attempting to write to or read the builder/ring files while
operations are in progress. This can be useful in environments where ring management has
been automated but the operator still needs to interact with the rings manually.

SEARCH

<search-value>
Can be of the form:
d<device_id>z<zone>-<ip>:<port>/<device_name>_<meta>

Any part is optional, but you must include at least one, examples:

d74 Matches the device id 74
z1 Matches devices in zone 1
z1-1.2.3.4 Matches devices in zone 1 with the ip 1.2.3.4
1.2.3.4 Matches devices in any zone with the ip 1.2.3.4
z1:5678 Matches devices in zone 1 using port 5678
:5678 Matches devices that use port 5678
/sdb1 Matches devices with the device name sdb1
_shiny Matches devices with shiny in the meta data
_'snet: 5.6.7.8' Matches devices with snet: 5.6.7.8 in the meta data
[::1] Matches devices in any zone with the ip ::1
z1-[::1]:5678 Matches devices in zone 1 with ip ::1 and port 5678

Most specific example:

d74z1-1.2.3.4:5678/sdb1_"snet: 5.6.7.8"

Nerd explanation:

All items require their single character prefix except the ip, in which case the -
is optional unless the device id or zone is also included.

COMMANDS

<builder_file>
Shows information about the ring and the devices within.

search <search-value>
Shows information about matching devices.

add z<zone>-<ip>:<port>/<device_name>_<meta> <weight>
add r<region>z<zone>-<ip>:<port>/<device_name>_<meta> <weight>
add -r <region> -z <zone> -i <ip> -p <port> -d <device_name> -m <meta> -w <weight>
Adds a device to the ring with the given information. No partitions will be assigned
to the new device until after running 'rebalance'. This is so you can make multiple
device changes and rebalance them all just once.

create <part_power> <replicas> <min_part_hours>
Creates <builder_file> with 2^<part_power> partitions and <replicas>.
<min_part_hours> is number of hours to restrict moving a partition more than once.

list_parts <search-value> [<search-value>] ..
Returns a 2 column list of all the partitions that are assigned to any of the devices
matching the search values given. The first column is the assigned partition number
and the second column is the number of device matches for that partition. The list is
ordered from most number of matches to least. If there are a lot of devices to match
against, this command could take a while to run.

rebalance
Attempts to rebalance the ring by reassigning partitions that haven't been recently
reassigned.

remove <search-value>
Removes the device(s) from the ring. This should normally just be used for a device
that has failed. For a device you wish to decommission, it's best to set its weight
to 0, wait for it to drain all its data, then use this remove command. This will not
take effect until after running 'rebalance'. This is so you can make multiple device
changes and rebalance them all just once.

set_info <search-value> <ip>:<port>/<device_name>_<meta>
Resets the device's information. This information isn't used to assign partitions, so
you can use 'write_ring' afterward to rewrite the current ring with the newer device
information. Any of the parts are optional in the final
<ip>:<port>/<device_name>_<meta> parameter; just give what you want to change. For
instance set_info d74 _"snet: 5.6.7.8" would just update the meta data for device id
74.

set_min_part_hours <hours>
Changes the <min_part_hours> to the given <hours>. This should be set to however long
a full replication/update cycle takes. We're working on a way to determine this more
easily than scanning logs.

set_weight <search-value> <weight>
Resets the device's weight. No partitions will be reassigned to or from the device
until after running 'rebalance'. This is so you can make multiple device changes and
rebalance them all just once.

validate
Just runs the validation routines on the ring.

write_ring
Just rewrites the distributable ring file. This is done automatically after a
successful rebalance, so really this is only useful after one or more 'set_info'
calls when no rebalance is needed but you want to send out the new device
information.

Quick list: add create list_parts rebalance remove search set_info
set_min_part_hours set_weight validate write_ring

Exit codes: 0 = ring changed, 1 = ring did not change, 2 = error

DOCUMENTATION

More in depth documentation about the swift ring and also Openstack-Swift as a whole can
be found at http://swift.openstack.org/overview_ring.html,
http://swift.openstack.org/admin_guide.html#managing-the-rings and
http://swift.openstack.org

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