Deployment Guide¶
This document provides general guidance for deploying and configuring Swift. Detailed descriptions of configuration options can be found in the configuration documentation.
Hardware Considerations¶
Swift is designed to run on commodity hardware. RAID on the storage drives is not required and not recommended. Swift’s disk usage pattern is the worst case possible for RAID, and performance degrades very quickly using RAID 5 or 6.
Deployment Options¶
The Swift services run completely autonomously, which provides for a lot of flexibility when architecting the hardware deployment for Swift. The 4 main services are:
Proxy Services
Object Services
Container Services
Account Services
The Proxy Services are more CPU and network I/O intensive. If you are using 10g networking to the proxy, or are terminating SSL traffic at the proxy, greater CPU power will be required.
The Object, Container, and Account Services (Storage Services) are more disk and network I/O intensive.
The easiest deployment is to install all services on each server. There is nothing wrong with doing this, as it scales each service out horizontally.
Alternatively, one set of servers may be dedicated to the Proxy Services and a different set of servers dedicated to the Storage Services. This allows faster networking to be configured to the proxy than the storage servers, and keeps load balancing to the proxies more manageable. Storage Services scale out horizontally as storage servers are added, and the overall API throughput can be scaled by adding more proxies.
If you need more throughput to either Account or Container Services, they may each be deployed to their own servers. For example you might use faster (but more expensive) SAS or even SSD drives to get faster disk I/O to the databases.
A high-availability (HA) deployment of Swift requires that multiple proxy servers are deployed and requests are load-balanced between them. Each proxy server instance is stateless and able to respond to requests for the entire cluster.
Load balancing and network design is left as an exercise to the reader, but this is a very important part of the cluster, so time should be spent designing the network for a Swift cluster.
Web Front End Options¶
Swift comes with an integral web front end. However, it can also be deployed as a request processor of an Apache2 using mod_wsgi as described in Apache Deployment Guide.
Preparing the Ring¶
The first step is to determine the number of partitions that will be in the ring. We recommend that there be a minimum of 100 partitions per drive to insure even distribution across the drives. A good starting point might be to figure out the maximum number of drives the cluster will contain, and then multiply by 100, and then round up to the nearest power of two.
For example, imagine we are building a cluster that will have no more than 5,000 drives. That would mean that we would have a total number of 500,000 partitions, which is pretty close to 2^19, rounded up.
It is also a good idea to keep the number of partitions small (relatively). The more partitions there are, the more work that has to be done by the replicators and other backend jobs and the more memory the rings consume in process. The goal is to find a good balance between small rings and maximum cluster size.
The next step is to determine the number of replicas to store of the data. Currently it is recommended to use 3 (as this is the only value that has been tested). The higher the number, the more storage that is used but the less likely you are to lose data.
It is also important to determine how many zones the cluster should have. It is recommended to start with a minimum of 5 zones. You can start with fewer, but our testing has shown that having at least five zones is optimal when failures occur. We also recommend trying to configure the zones at as high a level as possible to create as much isolation as possible. Some example things to take into consideration can include physical location, power availability, and network connectivity. For example, in a small cluster you might decide to split the zones up by cabinet, with each cabinet having its own power and network connectivity. The zone concept is very abstract, so feel free to use it in whatever way best isolates your data from failure. Each zone exists in a region.
A region is also an abstract concept that may be used to distinguish between geographically separated areas as well as can be used within same datacenter. Regions and zones are referenced by a positive integer.
You can now start building the ring with:
swift-ring-builder <builder_file> create <part_power> <replicas> <min_part_hours>
This will start the ring build process creating the <builder_file> with 2^<part_power> partitions. <min_part_hours> is the time in hours before a specific partition can be moved in succession (24 is a good value for this).
Devices can be added to the ring with:
swift-ring-builder <builder_file> add r<region>z<zone>-<ip>:<port>/<device_name>_<meta> <weight>
This will add a device to the ring where <builder_file> is the name of the builder file that was created previously, <region> is the number of the region the zone is in, <zone> is the number of the zone this device is in, <ip> is the ip address of the server the device is in, <port> is the port number that the server is running on, <device_name> is the name of the device on the server (for example: sdb1), <meta> is a string of metadata for the device (optional), and <weight> is a float weight that determines how many partitions are put on the device relative to the rest of the devices in the cluster (a good starting point is 100.0 x TB on the drive).Add each device that will be initially in the cluster.
Once all of the devices are added to the ring, run:
swift-ring-builder <builder_file> rebalance
This will distribute the partitions across the drives in the ring. It is important whenever making changes to the ring to make all the changes required before running rebalance. This will ensure that the ring stays as balanced as possible, and as few partitions are moved as possible.
The above process should be done to make a ring for each storage service (Account, Container and Object). The builder files will be needed in future changes to the ring, so it is very important that these be kept and backed up. The resulting .tar.gz ring file should be pushed to all of the servers in the cluster. For more information about building rings, running swift-ring-builder with no options will display help text with available commands and options. More information on how the ring works internally can be found in the Ring Overview.
Running object-servers Per Disk¶
The lack of true asynchronous file I/O on Linux leaves the object-server workers vulnerable to misbehaving disks. Because any object-server worker can service a request for any disk, and a slow I/O request blocks the eventlet hub, a single slow disk can impair an entire storage node. This also prevents object servers from fully utilizing all their disks during heavy load.
Another way to get full I/O isolation is to give each disk on a storage node a different port in the storage policy rings. Then set the servers_per_port option in the object-server config. NOTE: while the purpose of this config setting is to run one or more object-server worker processes per disk, the implementation just runs object-servers per unique port of local devices in the rings. The deployer must combine this option with appropriately-configured rings to benefit from this feature.
Here’s an example (abbreviated) old-style ring (2 node cluster with 2 disks each):
Devices: id region zone ip address port replication ip replication port name
0 1 1 1.1.0.1 6200 1.1.0.1 6200 d1
1 1 1 1.1.0.1 6200 1.1.0.1 6200 d2
2 1 2 1.1.0.2 6200 1.1.0.2 6200 d3
3 1 2 1.1.0.2 6200 1.1.0.2 6200 d4
And here’s the same ring set up for servers_per_port
:
Devices: id region zone ip address port replication ip replication port name
0 1 1 1.1.0.1 6200 1.1.0.1 6200 d1
1 1 1 1.1.0.1 6201 1.1.0.1 6201 d2
2 1 2 1.1.0.2 6200 1.1.0.2 6200 d3
3 1 2 1.1.0.2 6201 1.1.0.2 6201 d4
When migrating from normal to servers_per_port
, perform these steps in order:
Upgrade Swift code to a version capable of doing
servers_per_port
.Enable
servers_per_port
with a value greater than zero.Restart
swift-object-server
processes with a SIGHUP. At this point, you will have theservers_per_port
number ofswift-object-server
processes serving all requests for all disks on each node. This preserves availability, but you should perform the next step as quickly as possible.Push out new rings that actually have different ports per disk on each server. One of the ports in the new ring should be the same as the port used in the old ring (“6200” in the example above). This will cover existing proxy-server processes who haven’t loaded the new ring yet. They can still talk to any storage node regardless of whether or not that storage node has loaded the ring and started object-server processes on the new ports.
If you do not run a separate object-server for replication, then this setting must be available to the object-replicator and object-reconstructor (i.e. appear in the [DEFAULT] config section).
General Service Configuration¶
Most Swift services fall into two categories. Swift’s wsgi servers and background daemons.
For more information specific to the configuration of Swift’s wsgi servers with paste deploy see General Server Configuration.
Configuration for servers and daemons can be expressed together in the same file for each type of server, or separately. If a required section for the service trying to start is missing there will be an error. The sections not used by the service are ignored.
Consider the example of an object storage node. By convention, configuration
for the object-server, object-updater, object-replicator, object-auditor, and
object-reconstructor exist in a single file /etc/swift/object-server.conf
:
[DEFAULT]
reclaim_age = 604800
[pipeline:main]
pipeline = object-server
[app:object-server]
use = egg:swift#object
[object-replicator]
[object-updater]
[object-auditor]
Swift services expect a configuration path as the first argument:
$ swift-object-auditor
Usage: swift-object-auditor CONFIG [options]
Error: missing config path argument
If you omit the object-auditor section this file could not be used as the
configuration path when starting the swift-object-auditor
daemon:
$ swift-object-auditor /etc/swift/object-server.conf
Unable to find object-auditor config section in /etc/swift/object-server.conf
If the configuration path is a directory instead of a file all of the files in the directory with the file extension “.conf” will be combined to generate the configuration object which is delivered to the Swift service. This is referred to generally as “directory based configuration”.
Directory based configuration leverages ConfigParser’s native multi-file support. Files ending in “.conf” in the given directory are parsed in lexicographical order. Filenames starting with ‘.’ are ignored. A mixture of file and directory configuration paths is not supported - if the configuration path is a file only that file will be parsed.
The Swift service management tool swift-init
has adopted the convention of
looking for /etc/swift/{type}-server.conf.d/
if the file
/etc/swift/{type}-server.conf
file does not exist.
When using directory based configuration, if the same option under the same section appears more than once in different files, the last value parsed is said to override previous occurrences. You can ensure proper override precedence by prefixing the files in the configuration directory with numerical values.:
/etc/swift/
default.base
object-server.conf.d/
000_default.conf -> ../default.base
001_default-override.conf
010_server.conf
020_replicator.conf
030_updater.conf
040_auditor.conf
You can inspect the resulting combined configuration object using the
swift-config
command line tool
General Server Configuration¶
Swift uses paste.deploy (https://pypi.org/project/Paste/) to manage server configurations. Detailed descriptions of configuration options can be found in the configuration documentation.
Default configuration options are set in the [DEFAULT]
section, and any
options specified there can be overridden in any of the other sections BUT
ONLY BY USING THE SYNTAX set option_name = value
. This is the unfortunate
way paste.deploy works and I’ll try to explain it in full.
First, here’s an example paste.deploy configuration file:
[DEFAULT]
name1 = globalvalue
name2 = globalvalue
name3 = globalvalue
set name4 = globalvalue
[pipeline:main]
pipeline = myapp
[app:myapp]
use = egg:mypkg#myapp
name2 = localvalue
set name3 = localvalue
set name5 = localvalue
name6 = localvalue
The resulting configuration that myapp receives is:
global {'__file__': '/etc/mypkg/wsgi.conf', 'here': '/etc/mypkg',
'name1': 'globalvalue',
'name2': 'globalvalue',
'name3': 'localvalue',
'name4': 'globalvalue',
'name5': 'localvalue',
'set name4': 'globalvalue'}
local {'name6': 'localvalue'}
So, name1
got the global value which is fine since it’s only in the DEFAULT
section anyway.
name2
got the global value from DEFAULT
even though it appears to be
overridden in the app:myapp
subsection. This is just the unfortunate way
paste.deploy works (at least at the time of this writing.)
name3
got the local value from the app:myapp
subsection because it is using
the special paste.deploy syntax of set option_name = value
. So, if you want
a default value for most app/filters but want to override it in one
subsection, this is how you do it.
name4
got the global value from DEFAULT
since it’s only in that section
anyway. But, since we used the set
syntax in the DEFAULT
section even
though we shouldn’t, notice we also got a set name4
variable. Weird, but
probably not harmful.
name5
got the local value from the app:myapp
subsection since it’s only
there anyway, but notice that it is in the global configuration and not the
local configuration. This is because we used the set
syntax to set the
value. Again, weird, but not harmful since Swift just treats the two sets of
configuration values as one set anyway.
name6
got the local value from app:myapp
subsection since it’s only there,
and since we didn’t use the set
syntax, it’s only in the local
configuration and not the global one. Though, as indicated above, there is no
special distinction with Swift.
That’s quite an explanation for something that should be so much simpler, but it might be important to know how paste.deploy interprets configuration files. The main rule to remember when working with Swift configuration files is:
Note
Use the set option_name = value
syntax in subsections if the option is
also set in the [DEFAULT]
section. Don’t get in the habit of always
using the set
syntax or you’ll probably mess up your non-paste.deploy
configuration files.
Per policy configuration¶
Some proxy-server configuration options may be overridden for individual Storage Policies by including per-policy config section(s). These options are:
sorting_method
read_affinity
write_affinity
write_affinity_node_count
write_affinity_handoff_delete_count
The per-policy config section name must be of the form:
[proxy-server:policy:<policy index>]
Note
The per-policy config section name should refer to the policy index, not the policy name.
Note
The first part of proxy-server config section name must match the name of
the proxy-server config section. This is typically proxy-server
as
shown above, but if different then the names of any per-policy config
sections must be changed accordingly.
The value of an option specified in a per-policy section will override any value given in the proxy-server section for that policy only. Otherwise the value of these options will be that specified in the proxy-server section.
For example, the following section provides policy-specific options for a
policy with index 3
:
[proxy-server:policy:3]
sorting_method = affinity
read_affinity = r2=1
write_affinity = r2
write_affinity_node_count = 1 * replicas
write_affinity_handoff_delete_count = 2
Note
It is recommended that per-policy config options are not included in the
[DEFAULT]
section. If they are then the following behavior applies.
Per-policy config sections will inherit options in the [DEFAULT]
section of the config file, and any such inheritance will take precedence
over inheriting options from the proxy-server config section.
Per-policy config section options will override options in the
[DEFAULT]
section. Unlike the behavior described under General Server
Configuration for paste-deploy filter
and app
sections, the
set
keyword is not required for options to override in per-policy
config sections.
For example, given the following settings in a config file:
[DEFAULT]
sorting_method = affinity
read_affinity = r0=100
write_affinity = r0
[app:proxy-server]
use = egg:swift#proxy
# use of set keyword here overrides [DEFAULT] option
set read_affinity = r1=100
# without set keyword, [DEFAULT] option overrides in a paste-deploy section
write_affinity = r1
[proxy-server:policy:0]
sorting_method = affinity
# set keyword not required here to override [DEFAULT] option
write_affinity = r1
would result in policy with index 0
having settings:
read_affinity = r0=100
(inherited from the[DEFAULT]
section)write_affinity = r1
(specified in the policy 0 section)
and any other policy would have the default settings of:
read_affinity = r1=100
(set in the proxy-server section)write_affinity = r0
(inherited from the[DEFAULT]
section)
Proxy Middlewares¶
Many features in Swift are implemented as middleware in the proxy-server
pipeline. See Middleware and the proxy-server.conf-sample
file for
more information. In particular, the use of some type of authentication
and authorization middleware is highly recommended.
Memcached Considerations¶
Several of the Services rely on Memcached for caching certain types of lookups,
such as auth tokens, and container/account existence. Swift does not do any
caching of actual object data. Memcached should be able to run on any servers
that have available RAM and CPU. Typically Memcached is run on the proxy
servers. The memcache_servers
config option in the proxy-server.conf
should contain all memcached servers.
System Time¶
Time may be relative but it is relatively important for Swift! Swift uses timestamps to determine which is the most recent version of an object. It is very important for the system time on each server in the cluster to by synced as closely as possible (more so for the proxy server, but in general it is a good idea for all the servers). Typical deployments use NTP with a local NTP server to ensure that the system times are as close as possible. This should also be monitored to ensure that the times do not vary too much.
General Service Tuning¶
Most services support either a workers
or concurrency
value in the
settings. This allows the services to make effective use of the cores
available. A good starting point is to set the concurrency level for the proxy
and storage services to 2 times the number of cores available. If more than
one service is sharing a server, then some experimentation may be needed to
find the best balance.
For example, one operator reported using the following settings in a production Swift cluster:
Proxy servers have dual quad core processors (i.e. 8 cores); testing has shown 16 workers to be a pretty good balance when saturating a 10g network and gives good CPU utilization.
Storage server processes all run together on the same servers. These servers have dual quad core processors, for 8 cores total. The Account, Container, and Object servers are run with 8 workers each. Most of the background jobs are run at a concurrency of 1, with the exception of the replicators which are run at a concurrency of 2.
The max_clients
parameter can be used to adjust the number of client
requests an individual worker accepts for processing. The fewer requests being
processed at one time, the less likely a request that consumes the worker’s
CPU time, or blocks in the OS, will negatively impact other requests. The more
requests being processed at one time, the more likely one worker can utilize
network and disk capacity.
On systems that have more cores, and more memory, where one can afford to run more workers, raising the number of workers and lowering the maximum number of clients serviced per worker can lessen the impact of CPU intensive or stalled requests.
The nice_priority
parameter can be used to set program scheduling priority.
The ionice_class
and ionice_priority
parameters can be used to set I/O scheduling
class and priority on the systems that use an I/O scheduler that supports
I/O priorities. As at kernel 2.6.17 the only such scheduler is the Completely
Fair Queuing (CFQ) I/O scheduler. If you run your Storage servers all together
on the same servers, you can slow down the auditors or prioritize
object-server I/O via these parameters (but probably do not need to change
it on the proxy). It is a new feature and the best practices are still
being developed. On some systems it may be required to run the daemons as root.
For more info also see setpriority(2) and ioprio_set(2).
The above configuration setting should be taken as suggestions and testing of configuration settings should be done to ensure best utilization of CPU, network connectivity, and disk I/O.
Filesystem Considerations¶
Swift is designed to be mostly filesystem agnostic–the only requirement being that the filesystem supports extended attributes (xattrs). After thorough testing with our use cases and hardware configurations, XFS was the best all-around choice. If you decide to use a filesystem other than XFS, we highly recommend thorough testing.
For distros with more recent kernels (for example Ubuntu 12.04 Precise), we recommend using the default settings (including the default inode size of 256 bytes) when creating the file system:
mkfs.xfs -L D1 /dev/sda1
In the last couple of years, XFS has made great improvements in how inodes are allocated and used. Using the default inode size no longer has an impact on performance.
For distros with older kernels (for example Ubuntu 10.04 Lucid), some settings can dramatically impact performance. We recommend the following when creating the file system:
mkfs.xfs -i size=1024 -L D1 /dev/sda1
Setting the inode size is important, as XFS stores xattr data in the inode. If the metadata is too large to fit in the inode, a new extent is created, which can cause quite a performance problem. Upping the inode size to 1024 bytes provides enough room to write the default metadata, plus a little headroom.
The following example mount options are recommended when using XFS:
mount -t xfs -o noatime -L D1 /srv/node/d1
We do not recommend running Swift on RAID, but if you are using RAID it is also important to make sure that the proper sunit and swidth settings get set so that XFS can make most efficient use of the RAID array.
For a standard Swift install, all data drives are mounted directly under
/srv/node
(as can be seen in the above example of mounting label D1
as /srv/node/d1
). If you choose to mount the drives in another directory,
be sure to set the devices
config option in all of the server configs to
point to the correct directory.
The mount points for each drive in /srv/node/
should be owned by the root user
almost exclusively (root:root 755
). This is required to prevent rsync from
syncing files into the root drive in the event a drive is unmounted.
Swift uses system calls to reserve space for new objects being written into
the system. If your filesystem does not support fallocate()
or
posix_fallocate()
, be sure to set the disable_fallocate = true
config
parameter in account, container, and object server configs.
Most current Linux distributions ship with a default installation of updatedb.
This tool runs periodically and updates the file name database that is used by
the GNU locate tool. However, including Swift object and container database
files is most likely not required and the periodic update affects the
performance quite a bit. To disable the inclusion of these files add the path
where Swift stores its data to the setting PRUNEPATHS in /etc/updatedb.conf
:
PRUNEPATHS="... /tmp ... /var/spool ... /srv/node"
General System Tuning¶
The following changes have been found to be useful when running Swift on Ubuntu Server 10.04.
The following settings should be in /etc/sysctl.conf
:
# disable TIME_WAIT.. wait..
net.ipv4.tcp_tw_recycle=1
net.ipv4.tcp_tw_reuse=1
# disable syn cookies
net.ipv4.tcp_syncookies = 0
# double amount of allowed conntrack
net.netfilter.nf_conntrack_max = 262144
To load the updated sysctl settings, run sudo sysctl -p
.
A note about changing the TIME_WAIT values. By default the OS will hold a port open for 60 seconds to ensure that any remaining packets can be received. During high usage, and with the number of connections that are created, it is easy to run out of ports. We can change this since we are in control of the network. If you are not in control of the network, or do not expect high loads, then you may not want to adjust those values.
Logging Considerations¶
Swift is set up to log directly to syslog. Every service can be configured
with the log_facility
option to set the syslog log facility destination.
We recommended using syslog-ng to route the logs to specific log
files locally on the server and also to remote log collecting servers.
Additionally, custom log handlers can be used via the custom_log_handlers
setting.