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debian-mirror-gitlab/doc/administration/nfs.md
Pirate Praveen 98b945ec52 New upstream version 13.9.3+ds1
2021-03-11 19:13:27 +05:30

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---
stage: Enablement
group: Distribution
info: 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
type: reference
---
# Using NFS with GitLab
NFS can be used as an alternative for object storage but this isn't typically
recommended for performance reasons. Note however it is required for [GitLab
Pages](https://gitlab.com/gitlab-org/gitlab-pages/-/issues/196).
For data objects such as LFS, Uploads, Artifacts, etc., an [Object Storage service](object_storage.md)
is recommended over NFS where possible, due to better performance.
WARNING:
From GitLab 13.0, using NFS for Git repositories is deprecated.
From GitLab 14.0, technical support for NFS for Git repositories
will no longer be provided. Upgrade to [Gitaly Cluster](gitaly/praefect.md)
as soon as possible.
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](operations/filesystem_benchmarking.md).
## 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](https://bugzilla.redhat.com/show_bug.cgi?id=1783554) that causes
[uploads to fail to copy over NFS](https://gitlab.com/gitlab-org/gitlab/-/issues/218999). The
following GitLab versions include a fix to work properly with that
kernel version:
- [12.10.12](https://about.gitlab.com/releases/2020/06/25/gitlab-12-10-12-released/)
- [13.0.7](https://about.gitlab.com/releases/2020/06/25/gitlab-13-0-7-released/)
- [13.1.1](https://about.gitlab.com/releases/2020/06/24/gitlab-13-1-1-released/)
- 13.2 and up
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](operations/fast_ssh_key_lookup.md) feature can improve
performance of GitLab instances even if they're using block storage.
[Fast SSH key lookup](operations/fast_ssh_key_lookup.md) 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](https://gitlab.com/groups/gitlab-org/-/epics/3104).
## NFS server
Installing the `nfs-kernel-server` package allows you to share directories with
the clients running the GitLab application:
```shell
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 the `root` user to `nobody`. This is
a good security measure when NFS shares will be accessed by many different
users. However, in this case only GitLab will use the NFS share so it
is safe. GitLab recommends the `no_root_squash` setting 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 as `root` but as non-privileged
users. The recommendation for `no_root_squash` is to allow the Omnibus package
to set ownership and permissions on files, as needed. In some cases where the
`no_root_squash` option is not available, the `root` flag 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](https://library.netapp.com/ecmdocs/ECMP1401220/html/GUID-24367A9F-E17B-4725-ADC1-02D86F56F78E.html)
- For non-NetApp devices, disable NFSv4 `idmapping` by performing opposite of [enable NFSv4 idmapper](https://wiki.archlinux.org/index.php/NFS#Enabling_NFSv4_idmapping)
### Disable NFS server delegation
We recommend that all NFS users disable the NFS server delegation feature. This
is to avoid a [Linux kernel bug](https://bugzilla.redhat.com/show_bug.cgi?id=1552203)
which causes NFS clients to slow precipitously due to
[excessive network traffic from numerous `TEST_STATEID` NFS messages](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/52017).
To disable NFS server delegation, do the following:
1. On the NFS server, run:
```shell
echo 0 > /proc/sys/fs/leases-enable
sysctl -w fs.leases-enable=0
```
1. 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](https://github.com/torvalds/linux/commit/95da1b3a5aded124dd1bda1e3cdb876184813140).
Red Hat Enterprise 7 [shipped a kernel update](https://access.redhat.com/errata/RHSA-2019:2029)
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](gitaly/index.md#direct-access-to-git-in-gitlab) using
[Rugged](https://github.com/libgit2/rugged).
NOTE:
From GitLab 12.1, it will automatically be detected if Rugged can and should be used per storage.
If you previously enabled Rugged using the feature flag, you will need to unset the feature flag by using:
```shell
sudo gitlab-rake gitlab:features:unset_rugged
```
If the Rugged feature flag is explicitly set to either `true` or `false`, GitLab will use 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`](https://docs.gitlab.com/omnibus/settings/puma.html#puma-settings).
If you want to use Rugged with Puma thread count more than `1`, Rugged can be enabled using the [feature flag](../development/gitaly.md#legacy-rugged-code).
## NFS client
The `nfs-common` provides NFS functionality without installing server components which
we don't need running on the application nodes.
```shell
apt-get update
apt-get install nfs-common
```
### Mount options
Here is an example snippet to add to `/etc/fstab`:
```plaintext
10.1.0.1:/var/opt/gitlab/.ssh /var/opt/gitlab/.ssh nfs4 defaults,vers=4.1,hard,rsize=1048576,wsize=1048576,noatime,nofail,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,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,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,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,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](https://gitlab.com/gitlab-org/gitaly/-/issues/1339) 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](#soft-mount-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](https://linux.die.net/man/5/nfs) 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](http://wiki.scn.sap.com/wiki/x/PARnFQ) and NetApp's
[knowledge base](https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/What_are_the_differences_between_hard_mount_and_soft_mount),
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` will cause 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](https://access.redhat.com/solutions/157873).
### 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.
```plaintext
mountpoint
└── gitlab-data
├── builds
├── git-data
├── shared
└── uploads
```
To do so, we'll need to 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:
```ruby
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'll 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`:
```shell
/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 will require manually making sure the data directories
are empty before attempting a restore. Read more about the
[restore prerequisites](../raketasks/backup_restore.md).
### Multiple NFS mounts
When using default Omnibus configuration you will 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 will account 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, etc. 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](https://docs.gitlab.com/omnibus/settings/logs.html#udp-log-shipping-gitlab-enterprise-edition-only).
Having multiple NFS mounts will require manually making sure the data directories
are empty before attempting a restore. Read more about the
[restore prerequisites](../raketasks/backup_restore.md).
## Testing NFS
Once you've set up the NFS server and client, you can verify NFS is configured correctly
by testing the following commands:
```shell
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 will need to reconfigure that firewall to allow NFS communication.
[This guide from TDLP](https://tldp.org/HOWTO/NFS-HOWTO/security.html#FIREWALLS)
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.
```shell
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:
From GitLab 13.0, using NFS for Git repositories is deprecated. In GitLab 14.0,
support for NFS for Git repositories is scheduled to be removed. Upgrade to
[Gitaly Cluster](gitaly/praefect.md) as soon as possible.
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](https://gitlab.com/gitlab-org/gitaly/-/issues/2589). 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 will still be significant. As noted above, we strongly recommend upgrading to
[Gitaly Cluster](gitaly/praefect.md) as soon as possible.
### Avoid using AWS's Elastic File System (EFS)
GitLab strongly recommends against using AWS Elastic File System (EFS).
Our support team will not be able to assist on performance issues related to
file system access.
Customers and users have reported that AWS EFS does not perform well for the GitLab
use-case. Workloads where many small files are written in a serialized manner, like `git`,
are not well-suited for EFS. EBS with an NFS server on top will perform much better.
If you do choose to use EFS, avoid storing GitLab log files (e.g. 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 another person's experience with EFS, see this [Commit Brooklyn 2019 video](https://youtu.be/K6OS8WodRBQ?t=313).
### 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](https://www.postgresql.org/docs/current/creating-cluster.html#CREATING-CLUSTER-NFS):
>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](postgresql/replication_and_failover.md).
## 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`:
```shell
sudo perf trace -e 'nfs4:*' -p $(pgrep -fd ',' puma && pgrep -fd ',' unicorn)
```
On Ubuntu 16.04, use:
```shell
sudo perf trace --no-syscalls --event 'nfs4:*' -p $(pgrep -fd ',' puma && pgrep -fd ',' unicorn)
```
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