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| stage | group | info | type |
|---|---|---|---|
| Enablement | Distribution | To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments | reference |
Using NFS with GitLab (FREE SELF)
NFS can be used as an alternative for object storage but this isn't typically recommended for performance reasons.
For data objects such as LFS, Uploads, Artifacts, and so on, an Object Storage service is recommended over NFS where possible, due to better performance.
File system performance can impact overall GitLab performance, especially for actions that read or write to Git repositories. For steps you can use to test file system performance, see File System Performance Benchmarking.
Gitaly and NFS deprecation
Engineering support for NFS for Git repositories is deprecated. Technical support is planned to be unavailable from GitLab 15.0. No further enhancements are planned for this feature.
Read:
- The Gitaly and NFS deprecation notice.
- About the correct mount options to use.
Known kernel version incompatibilities
RedHat Enterprise Linux (RHEL) and CentOS v7.7 and v7.8 ship with kernel
version 3.10.0-1127, which contains a
bug that causes
uploads to fail to copy over NFS. The
following GitLab versions include a fix to work properly with that
kernel version:
If you are using that kernel version, be sure to upgrade GitLab to avoid errors.
Fast lookup of authorized SSH keys
The fast SSH key lookup feature can improve performance of GitLab instances even if they're using block storage.
Fast SSH key lookup is a replacement for
authorized_keys (in /var/opt/gitlab/.ssh) using the GitLab database.
NFS increases latency, so fast lookup is recommended if /var/opt/gitlab
is moved to NFS.
We are investigating the use of fast lookup as the default.
NFS server
Installing the nfs-kernel-server package allows you to share directories with
the clients running the GitLab application:
sudo apt-get update
sudo apt-get install nfs-kernel-server
Required features
File locking: GitLab requires advisory file locking, which is only supported natively in NFS version 4. NFSv3 also supports locking as long as Linux Kernel 2.6.5+ is used. We recommend using version 4 and do not specifically test NFSv3.
Recommended options
When you define your NFS exports, we recommend you also add the following options:
no_root_squash- NFS normally changes therootuser tonobody. This is a good security measure when NFS shares are accessed by many different users. However, in this case only GitLab uses the NFS share so it is safe. GitLab recommends theno_root_squashsetting because we need to manage file permissions automatically. Without the setting you may receive errors when the Omnibus package tries to alter permissions. Note that GitLab and other bundled components do not run asrootbut as non-privileged users. The recommendation forno_root_squashis to allow the Omnibus package to set ownership and permissions on files, as needed. In some cases where theno_root_squashoption is not available, therootflag can achieve the same result.sync- Force synchronous behavior. Default is asynchronous and under certain circumstances it could lead to data loss if a failure occurs before data has synced.
Due to the complexities of running Omnibus with LDAP and the complexities of maintaining ID mapping without LDAP, in most cases you should enable numeric UIDs and GIDs (which is off by default in some cases) for simplified permission management between systems:
- NetApp instructions
- For non-NetApp devices, disable NFSv4
idmappingby performing opposite of enable NFSv4 idmapper
Disable NFS server delegation
We recommend that all NFS users disable the NFS server delegation feature. This
is to avoid a Linux kernel bug
which causes NFS clients to slow precipitously due to
excessive network traffic from numerous TEST_STATEID NFS messages.
To disable NFS server delegation, do the following:
-
On the NFS server, run:
echo 0 > /proc/sys/fs/leases-enable sysctl -w fs.leases-enable=0 -
Restart the NFS server process. For example, on CentOS run
service nfs restart.
NOTE: The kernel bug may be fixed in more recent kernels with this commit. Red Hat Enterprise 7 shipped a kernel update on August 6, 2019 that may also have resolved this problem. You may not need to disable NFS server delegation if you know you are using a version of the Linux kernel that has been fixed. That said, GitLab still encourages instance administrators to keep NFS server delegation disabled.
Improving NFS performance with GitLab
NFS performance with GitLab can in some cases be improved with direct Git access using Rugged.
NOTE: From GitLab 12.1, it automatically detects if Rugged can and should be used per storage.
If you previously enabled Rugged using the feature flag, you need to unset the feature flag by using:
sudo gitlab-rake gitlab:features:unset_rugged
If the Rugged feature flag is explicitly set to either true or false, GitLab uses the value explicitly set.
Improving NFS performance with Puma
NOTE:
From GitLab 12.7, Rugged is not automatically enabled if Puma thread count is greater than 1.
If you want to use Rugged with Puma, set Puma thread count to 1.
If you want to use Rugged with Puma thread count more than 1, Rugged can be enabled using the feature flag.
NFS client
The nfs-common provides NFS functionality without installing server components which
we don't need running on the application nodes.
apt-get update
apt-get install nfs-common
Mount options
Here is an example snippet to add to /etc/fstab:
10.1.0.1:/var/opt/gitlab/.ssh /var/opt/gitlab/.ssh nfs4 defaults,vers=4.1,hard,rsize=1048576,wsize=1048576,noatime,nofail,_netdev,lookupcache=positive 0 2
10.1.0.1:/var/opt/gitlab/gitlab-rails/uploads /var/opt/gitlab/gitlab-rails/uploads nfs4 defaults,vers=4.1,hard,rsize=1048576,wsize=1048576,noatime,nofail,_netdev,lookupcache=positive 0 2
10.1.0.1:/var/opt/gitlab/gitlab-rails/shared /var/opt/gitlab/gitlab-rails/shared nfs4 defaults,vers=4.1,hard,rsize=1048576,wsize=1048576,noatime,nofail,_netdev,lookupcache=positive 0 2
10.1.0.1:/var/opt/gitlab/gitlab-ci/builds /var/opt/gitlab/gitlab-ci/builds nfs4 defaults,vers=4.1,hard,rsize=1048576,wsize=1048576,noatime,nofail,_netdev,lookupcache=positive 0 2
10.1.0.1:/var/opt/gitlab/git-data /var/opt/gitlab/git-data nfs4 defaults,vers=4.1,hard,rsize=1048576,wsize=1048576,noatime,nofail,_netdev,lookupcache=positive 0 2
You can view information and options set for each of the mounted NFS file
systems by running nfsstat -m and cat /etc/fstab.
Note there are several options that you should consider using:
| Setting | Description |
|---|---|
vers=4.1 |
NFS v4.1 should be used instead of v4.0 because there is a Linux NFS client bug in v4.0 that can cause significant problems due to stale data. |
nofail |
Don't halt boot process waiting for this mount to become available |
lookupcache=positive |
Tells the NFS client to honor positive cache results but invalidates any negative cache results. Negative cache results cause problems with Git. Specifically, a git push can fail to register uniformly across all NFS clients. The negative cache causes the clients to 'remember' that the files did not exist previously. |
hard |
Instead of soft. Further details. |
cto |
cto is the default option, which you should use. Do not use nocto. Further details. |
_netdev |
Wait to mount file system until network is online. See also the high_availability['mountpoint'] option. |
soft mount option
It's recommended that you use hard in your mount options, unless you have a specific
reason to use soft.
On GitLab.com, we use soft because there were times when we had NFS servers
reboot and soft improved availability, but everyone's infrastructure is different.
If your NFS is provided by on-premise storage arrays with redundant controllers,
for example, you shouldn't need to worry about NFS server availability.
The NFS man page states:
"soft" timeout can cause silent data corruption in certain cases
Read the Linux man page to understand the difference,
and if you do use soft, ensure that you've taken steps to mitigate the risks.
If you experience behavior that might have been caused by
writes to disk on the NFS server not occurring, such as commits going missing,
use the hard option, because (from the man page):
use the soft option only when client responsiveness is more important than data integrity
Other vendors make similar recommendations, including
SAP and NetApp's
knowledge base,
they highlight that if the NFS client driver caches data, soft means there is no certainty if
writes by GitLab are actually on disk.
Mount points set with the option hard may not perform as well, and if the
NFS server goes down, hard causes processes to hang when interacting with
the mount point. Use SIGKILL (kill -9) to deal with hung processes.
The intr option
stopped working in the 2.6 kernel.
nocto mount option
Do not use nocto. Instead, use cto, which is the default.
When using nocto, the dentry cache is always used, up to acdirmax seconds (attribute cache time) from the time it's created.
This results in stale dentry cache issues with multiple clients, where each client can see a different (cached) version of a directory.
From the Linux man page, the important parts:
If the nocto option is specified, the client uses a non-standard heuristic to determine when files on the server have changed.
Using the nocto option may improve performance for read-only mounts, but should be used only if the data on the server changes only occasionally.
We have noticed this behavior in an issue about refs not found after a push, where newly added loose refs can be seen as missing on a different client with a local dentry cache, as described in this issue.
A single NFS mount
It's recommended to nest all GitLab data directories within a mount, that allows automatic restore of backups without manually moving existing data.
mountpoint
└── gitlab-data
├── builds
├── git-data
├── shared
└── uploads
To do so, configure Omnibus with the paths to each directory nested in the mount point as follows:
Mount /gitlab-nfs then use the following Omnibus
configuration to move each data location to a subdirectory:
git_data_dirs({"default" => { "path" => "/gitlab-nfs/gitlab-data/git-data"} })
gitlab_rails['uploads_directory'] = '/gitlab-nfs/gitlab-data/uploads'
gitlab_rails['shared_path'] = '/gitlab-nfs/gitlab-data/shared'
gitlab_ci['builds_directory'] = '/gitlab-nfs/gitlab-data/builds'
Run sudo gitlab-ctl reconfigure to start using the central location. Be aware
that if you had existing data, you need to manually copy or rsync it to
these new locations, and then restart GitLab.
Bind mounts
Alternatively to changing the configuration in Omnibus, bind mounts can be used to store the data on an NFS mount.
Bind mounts provide a way to specify just one NFS mount and then
bind the default GitLab data locations to the NFS mount. Start by defining your
single NFS mount point as you normally would in /etc/fstab. Let's assume your
NFS mount point is /gitlab-nfs. Then, add the following bind mounts in
/etc/fstab:
/gitlab-nfs/gitlab-data/git-data /var/opt/gitlab/git-data none bind 0 0
/gitlab-nfs/gitlab-data/.ssh /var/opt/gitlab/.ssh none bind 0 0
/gitlab-nfs/gitlab-data/uploads /var/opt/gitlab/gitlab-rails/uploads none bind 0 0
/gitlab-nfs/gitlab-data/shared /var/opt/gitlab/gitlab-rails/shared none bind 0 0
/gitlab-nfs/gitlab-data/builds /var/opt/gitlab/gitlab-ci/builds none bind 0 0
Using bind mounts requires you to manually make sure the data directories are empty before attempting a restore. Read more about the restore prerequisites.
Multiple NFS mounts
When using default Omnibus configuration you need to share 4 data locations between all GitLab cluster nodes. No other locations should be shared. The following are the 4 locations need to be shared:
| Location | Description | Default configuration |
|---|---|---|
/var/opt/gitlab/git-data |
Git repository data. This accounts for a large portion of your data | git_data_dirs({"default" => { "path" => "/var/opt/gitlab/git-data"} }) |
/var/opt/gitlab/gitlab-rails/uploads |
User uploaded attachments | gitlab_rails['uploads_directory'] = '/var/opt/gitlab/gitlab-rails/uploads' |
/var/opt/gitlab/gitlab-rails/shared |
Build artifacts, GitLab Pages, LFS objects, temp files, and so on. If you're using LFS this may also account for a large portion of your data | gitlab_rails['shared_path'] = '/var/opt/gitlab/gitlab-rails/shared' |
/var/opt/gitlab/gitlab-ci/builds |
GitLab CI/CD build traces | gitlab_ci['builds_directory'] = '/var/opt/gitlab/gitlab-ci/builds' |
Other GitLab directories should not be shared between nodes. They contain node-specific files and GitLab code that does not need to be shared. To ship logs to a central location consider using remote syslog. Omnibus GitLab packages provide configuration for UDP log shipping.
Having multiple NFS mounts requires you to manually make sure the data directories are empty before attempting a restore. Read more about the restore prerequisites.
Testing NFS
Once you've set up the NFS server and client, you can verify NFS is configured correctly by testing the following commands:
sudo mkdir /gitlab-nfs/test-dir
sudo chown git /gitlab-nfs/test-dir
sudo chgrp root /gitlab-nfs/test-dir
sudo chmod 0700 /gitlab-nfs/test-dir
sudo chgrp gitlab-www /gitlab-nfs/test-dir
sudo chmod 0751 /gitlab-nfs/test-dir
sudo chgrp git /gitlab-nfs/test-dir
sudo chmod 2770 /gitlab-nfs/test-dir
sudo chmod 2755 /gitlab-nfs/test-dir
sudo -u git mkdir /gitlab-nfs/test-dir/test2
sudo -u git chmod 2755 /gitlab-nfs/test-dir/test2
sudo ls -lah /gitlab-nfs/test-dir/test2
sudo -u git rm -r /gitlab-nfs/test-dir
Any Operation not permitted errors means you should investigate your NFS server export options.
NFS in a Firewalled Environment
If the traffic between your NFS server and NFS client(s) is subject to port filtering by a firewall, then you need to reconfigure that firewall to allow NFS communication.
This guide from TDLP covers the basics of using NFS in a firewalled environment. Additionally, we encourage you to search for and review the specific documentation for your operating system or distribution and your firewall software.
Example for Ubuntu:
Check that NFS traffic from the client is allowed by the firewall on the host by running
the command: sudo ufw status. If it's being blocked, then you can allow traffic from a specific
client with the command below.
sudo ufw allow from <client_ip_address> to any port nfs
Known issues
Upgrade to Gitaly Cluster or disable caching if experiencing data loss
WARNING: Engineering support for NFS for Git repositories is deprecated. Read the Gitaly and NFS deprecation notice.
Customers and users have reported data loss on high-traffic repositories when using NFS for Git repositories. For example, we have seen:
- Inconsistent updates after a push.
git ls-remotereturning the wrong (or no branches) causing Jenkins to intermittently re-run all pipelines for a repository.
The problem may be partially mitigated by adjusting caching using the following NFS client mount options:
| Setting | Description |
|---|---|
lookupcache=positive |
Tells the NFS client to honor positive cache results but invalidates any negative cache results. Negative cache results cause problems with Git. Specifically, a git push can fail to register uniformly across all NFS clients. The negative cache causes the clients to 'remember' that the files did not exist previously. |
actimeo=0 |
Sets the time to zero that the NFS client caches files and directories before requesting fresh information from a server. |
noac |
Tells the NFS client not to cache file attributes and forces application writes to become synchronous so that local changes to a file become visible on the server immediately. |
WARNING:
The actimeo=0 and noac options both result in a significant reduction in performance, possibly leading to timeouts.
You may be able to avoid timeouts and data loss using actimeo=0 and lookupcache=positive without noac, however
we expect the performance reduction is still significant. Upgrade to
Gitaly Cluster as soon as possible.
Avoid using cloud-based file systems
GitLab strongly recommends against using cloud-based file systems such as:
- AWS Elastic File System (EFS).
- Google Cloud Filestore.
- Azure Files.
Our support team cannot assist with performance issues related to cloud-based file system access.
Customers and users have reported that these file systems don't perform well for
the file system access GitLab requires. Workloads where many small files are written in
a serialized manner, like git, are not well suited to cloud-based file systems.
If you do choose to use these, avoid storing GitLab log files (for example, those in /var/log/gitlab)
there because this will also affect performance. We recommend that the log files be
stored on a local volume.
For more details on the experience of using a cloud-based file systems with GitLab, see this Commit Brooklyn 2019 video.
Avoid using CephFS and GlusterFS
GitLab strongly recommends against using CephFS and GlusterFS. These distributed file systems are not well-suited for the GitLab input/output access patterns because Git uses many small files and access times and file locking times to propagate will make Git activity very slow.
Avoid using PostgreSQL with NFS
GitLab strongly recommends against running your PostgreSQL database across NFS. The GitLab support team will not be able to assist on performance issues related to this configuration.
Additionally, this configuration is specifically warned against in the PostgreSQL Documentation:
PostgreSQL does nothing special for NFS file systems, meaning it assumes NFS behaves exactly like locally-connected drives. If the client or server NFS implementation does not provide standard file system semantics, this can cause reliability problems. Specifically, delayed (asynchronous) writes to the NFS server can cause data corruption problems.
For supported database architecture, see our documentation about configuring a database for replication and failover.
Troubleshooting
Finding the requests that are being made to NFS
In case of NFS-related problems, it can be helpful to trace
the file system requests that are being made by using perf:
sudo perf trace -e 'nfs4:*' -p $(pgrep -fd ',' puma)
On Ubuntu 16.04, use:
sudo perf trace --no-syscalls --event 'nfs4:*' -p $(pgrep -fd ',' puma)