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diff --git a/doc/administration/gitaly/index.md b/doc/administration/gitaly/index.md index b314fa85af7..1a8e18ca2b2 100644 --- a/doc/administration/gitaly/index.md +++ b/doc/administration/gitaly/index.md @@ -5,72 +5,296 @@ info: To determine the technical writer assigned to the Stage/Group associated w type: reference --- -# Gitaly +# Gitaly and Gitaly Cluster **(FREE SELF)** -[Gitaly](https://gitlab.com/gitlab-org/gitaly) is the service that provides high-level RPC access to -Git repositories. Without it, no GitLab components can read or write Git data. +[Gitaly](https://gitlab.com/gitlab-org/gitaly) provides high-level RPC access to Git repositories. +It is used by GitLab to read and write Git data. -In the Gitaly documentation: +Gitaly implements a client-server architecture: -- **Gitaly server** refers to any node that runs Gitaly itself. -- **Gitaly client** refers to any node that runs a process that makes requests of the - Gitaly server. Processes include, but are not limited to: +- A Gitaly server is any node that runs Gitaly itself. +- A Gitaly client is any node that runs a process that makes requests of the Gitaly server. These + include, but are not limited to: - [GitLab Rails application](https://gitlab.com/gitlab-org/gitlab). - [GitLab Shell](https://gitlab.com/gitlab-org/gitlab-shell). - [GitLab Workhorse](https://gitlab.com/gitlab-org/gitlab-workhorse). -GitLab end users do not have direct access to Gitaly. Gitaly manages only Git -repository access for GitLab. Other types of GitLab data aren't accessed using Gitaly. +The following illustrates the Gitaly client-server architecture: + +```mermaid +flowchart TD + subgraph Gitaly clients + A[GitLab Rails] + B[GitLab Workhorse] + C[GitLab Shell] + D[...] + end + + subgraph Gitaly + E[Git integration] + end + +F[Local filesystem] + +A -- gRPC --> Gitaly +B -- gRPC--> Gitaly +C -- gRPC --> Gitaly +D -- gRPC --> Gitaly + +E --> F +``` + +End users do not have direct access to Gitaly. Gitaly manages only Git repository access for GitLab. +Other types of GitLab data aren't accessed using Gitaly. <!-- vale gitlab.FutureTense = NO --> WARNING: -From GitLab 13.0, Gitaly support for NFS is deprecated. As of GitLab 14.0, NFS-related issues -with Gitaly will no longer be addressed. Upgrade to [Gitaly Cluster](praefect.md) as soon as -possible. Tools to [enable bulk moves](https://gitlab.com/groups/gitlab-org/-/epics/4916) -of projects to Gitaly Cluster are planned. +From GitLab 14.0, enhancements and bug fixes for NFS for Git repositories will no longer be +considered and customer technical support will be considered out of scope. +[Read more about Gitaly and NFS](#nfs-deprecation-notice). <!-- vale gitlab.FutureTense = YES --> -## Architecture +## Configure Gitaly -The following is a high-level architecture overview of how Gitaly is used. +Gitaly comes pre-configured with Omnibus GitLab, which is a configuration +[suitable for up to 1000 users](../reference_architectures/1k_users.md). For: - +- Omnibus GitLab installations for up to 2000 users, see [specific Gitaly configuration instructions](../reference_architectures/2k_users.md#configure-gitaly). +- Source installations or custom Gitaly installations, see [Configure Gitaly](#configure-gitaly). -## Configure Gitaly +GitLab installations for more than 2000 users should use Gitaly Cluster. + +NOTE: +If not set in GitLab, feature flags are read as false from the console and Gitaly uses their +default value. The default value depends on the GitLab version. + +## Gitaly Cluster + +Gitaly, the service that provides storage for Git repositories, can +be run in a clustered configuration to scale the Gitaly service and increase +fault tolerance. In this configuration, every Git repository is stored on every +Gitaly node in the cluster. + +Using a Gitaly Cluster increases fault tolerance by: + +- Replicating write operations to warm standby Gitaly nodes. +- Detecting Gitaly node failures. +- Automatically routing Git requests to an available Gitaly node. + +NOTE: +Technical support for Gitaly clusters is limited to GitLab Premium and Ultimate +customers. + +The availability objectives for Gitaly clusters are: + +- **Recovery Point Objective (RPO):** Less than 1 minute. + + Writes are replicated asynchronously. Any writes that have not been replicated + to the newly promoted primary are lost. + + [Strong consistency](praefect.md#strong-consistency) can be used to avoid loss in some + circumstances. + +- **Recovery Time Objective (RTO):** Less than 10 seconds. + Outages are detected by a health check run by each Praefect node every + second. Failover requires ten consecutive failed health checks on each + Praefect node. + + [Faster outage detection](https://gitlab.com/gitlab-org/gitaly/-/issues/2608) + is planned to improve this to less than 1 second. + +Gitaly Cluster supports: + +- [Strong consistency](praefect.md#strong-consistency) of the secondary replicas. +- [Automatic failover](praefect.md#automatic-failover-and-leader-election) from the primary to the secondary. +- Reporting of possible data loss if replication queue is non-empty. +- Marking repositories as [read only](praefect.md#read-only-mode) if data loss is detected to prevent data inconsistencies. + +Follow the [Gitaly Cluster epic](https://gitlab.com/groups/gitlab-org/-/epics/1489) +for improvements including +[horizontally distributing reads](https://gitlab.com/groups/gitlab-org/-/epics/2013). + +### Overview + +Git storage is provided through the Gitaly service in GitLab, and is essential +to the operation of the GitLab application. When the number of +users, repositories, and activity grows, it is important to scale Gitaly +appropriately by: + +- Increasing the available CPU and memory resources available to Git before + resource exhaustion degrades Git, Gitaly, and GitLab application performance. +- Increase available storage before storage limits are reached causing write + operations to fail. +- Improve fault tolerance by removing single points of failure. Git should be + considered mission critical if a service degradation would prevent you from + deploying changes to production. + +### Moving beyond NFS + +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 as soon as possible. + +[Network File System (NFS)](https://en.wikipedia.org/wiki/Network_File_System) +is not well suited to Git workloads which are CPU and IOPS sensitive. +Specifically: + +- Git is sensitive to file system latency. Even simple operations require many + read operations. Operations that are fast on block storage can become an order of + magnitude slower. This significantly impacts GitLab application performance. +- NFS performance optimizations that prevent the performance gap between + block storage and NFS being even wider are vulnerable to race conditions. We have observed + [data inconsistencies](https://gitlab.com/gitlab-org/gitaly/-/issues/2589) + in production environments caused by simultaneous writes to different NFS + clients. Data corruption is not an acceptable risk. + +Gitaly Cluster is purpose built to provide reliable, high performance, fault +tolerant Git storage. + +Further reading: + +- Blog post: [The road to Gitaly v1.0 (aka, why GitLab doesn't require NFS for storing Git data anymore)](https://about.gitlab.com/blog/2018/09/12/the-road-to-gitaly-1-0/) +- Blog post: [How we spent two weeks hunting an NFS bug in the Linux kernel](https://about.gitlab.com/blog/2018/11/14/how-we-spent-two-weeks-hunting-an-nfs-bug/) + +### Where Gitaly Cluster fits + +GitLab accesses [repositories](../../user/project/repository/index.md) through the configured +[repository storages](../repository_storage_paths.md). Each new repository is stored on one of the +repository storages based on their configured weights. Each repository storage is either: + +- A Gitaly storage served directly by Gitaly. These map to a directory on the file system of a + Gitaly node. +- A [virtual storage](#virtual-storage-or-direct-gitaly-storage) served by Praefect. A virtual + storage is a cluster of Gitaly storages that appear as a single repository storage. + +Virtual storages are a feature of Gitaly Cluster. They support replicating the repositories to +multiple storages for fault tolerance. Virtual storages can improve performance by distributing +requests across Gitaly nodes. Their distributed nature makes it viable to have a single repository +storage in GitLab to simplify repository management. + +### Components of Gitaly Cluster + +Gitaly Cluster consists of multiple components: + +- [Load balancer](praefect.md#load-balancer) for distributing requests and providing fault-tolerant access to + Praefect nodes. +- [Praefect](praefect.md#praefect) nodes for managing the cluster and routing requests to Gitaly nodes. +- [PostgreSQL database](praefect.md#postgresql) for persisting cluster metadata and [PgBouncer](praefect.md#pgbouncer), + recommended for pooling Praefect's database connections. +- Gitaly nodes to provide repository storage and Git access. + + + +In this example: + +- Repositories are stored on a virtual storage called `storage-1`. +- Three Gitaly nodes provide `storage-1` access: `gitaly-1`, `gitaly-2`, and `gitaly-3`. +- The three Gitaly nodes store data on their file systems. + +### Virtual storage or direct Gitaly storage + +Gitaly supports multiple models of scaling: + +- Clustering using Gitaly Cluster, where each repository is stored on multiple Gitaly nodes in the + cluster. Read requests are distributed between repository replicas and write requests are + broadcast to repository replicas. GitLab accesses virtual storage. +- Direct access to Gitaly storage using [repository storage paths](../repository_storage_paths.md), + where each repository is stored on the assigned Gitaly node. All requests are routed to this node. -Gitaly comes pre-configured with Omnibus GitLab. For more information on customizing your -Gitaly installation, see [Configure Gitaly](configure_gitaly.md). +The following is Gitaly set up to use direct access to Gitaly instead of Gitaly Cluster: -## Direct Git access bypassing Gitaly + -GitLab doesn't advise directly accessing Gitaly repositories stored on disk with -a Git client, because Gitaly is being continuously improved and changed. These -improvements may invalidate assumptions, resulting in performance degradation, instability, and even data loss. +In this example: -Gitaly has optimizations, such as the -[`info/refs` advertisement cache](https://gitlab.com/gitlab-org/gitaly/blob/master/doc/design_diskcache.md), -that rely on Gitaly controlling and monitoring access to repositories by using the -official gRPC interface. Likewise, Praefect has optimizations, such as fault -tolerance and distributed reads, that depend on the gRPC interface and -database to determine repository state. +- Each repository is stored on one of three Gitaly storages: `storage-1`, `storage-2`, + or `storage-3`. +- Each storage is serviced by a Gitaly node. +- The three Gitaly nodes store data in three separate hashed storage locations. -For these reasons, **accessing repositories directly is done at your own risk -and is not supported**. +Generally, virtual storage with Gitaly Cluster can replace direct Gitaly storage configurations, at +the expense of additional storage needed to store each repository on multiple Gitaly nodes. The +benefit of using Gitaly Cluster over direct Gitaly storage is: + +- Improved fault tolerance, because each Gitaly node has a copy of every repository. +- Improved resource utilization, reducing the need for over-provisioning for shard-specific peak + loads, because read loads are distributed across replicas. +- Manual rebalancing for performance is not required, because read loads are distributed across + replicas. +- Simpler management, because all Gitaly nodes are identical. + +Under some workloads, CPU and memory requirements may require a large fleet of Gitaly nodes. It +can be uneconomical to have one to one replication factor. + +A hybrid approach can be used in these instances, where each shard is configured as a smaller +cluster. [Variable replication factor](https://gitlab.com/groups/gitlab-org/-/epics/3372) is planned +to provide greater flexibility for extremely large GitLab instances. + +### Gitaly Cluster compared to Geo + +Gitaly Cluster and [Geo](../geo/index.md) both provide redundancy. However the redundancy of: + +- Gitaly Cluster provides fault tolerance for data storage and is invisible to the user. Users are + not aware when Gitaly Cluster is used. +- Geo provides [replication](../geo/index.md) and [disaster recovery](../geo/disaster_recovery/index.md) for + an entire instance of GitLab. Users know when they are using Geo for + [replication](../geo/index.md). Geo [replicates multiple data types](../geo/replication/datatypes.md#limitations-on-replicationverification), + including Git data. + +The following table outlines the major differences between Gitaly Cluster and Geo: + +| Tool | Nodes | Locations | Latency tolerance | Failover | Consistency | Provides redundancy for | +|:---------------|:---------|:----------|:-------------------|:----------------------------------------------------------------|:-----------------------------------------|:------------------------| +| Gitaly Cluster | Multiple | Single | Approximately 1 ms | [Automatic](praefect.md#automatic-failover-and-leader-election) | [Strong](praefect.md#strong-consistency) | Data storage in Git | +| Geo | Multiple | Multiple | Up to one minute | [Manual](../geo/disaster_recovery/index.md) | Eventual | Entire GitLab instance | + +For more information, see: + +- Geo [use cases](../geo/index.md#use-cases). +- Geo [architecture](../geo/index.md#architecture). + +### Architecture + +Praefect is a router and transaction manager for Gitaly, and a required +component for running a Gitaly Cluster. + + + +For more information, see [Gitaly High Availability (HA) Design](https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/design_ha.md). + +### Configure Gitaly Cluster + +For more information on configuring Gitaly Cluster, see [Configure Gitaly Cluster](praefect.md). + +## Do not bypass Gitaly + +GitLab doesn't advise directly accessing Gitaly repositories stored on disk with a Git client, +because Gitaly is being continuously improved and changed. These improvements may invalidate +your assumptions, resulting in performance degradation, instability, and even data loss. For example: + +- Gitaly has optimizations such as the [`info/refs` advertisement cache](https://gitlab.com/gitlab-org/gitaly/blob/master/doc/design_diskcache.md), + that rely on Gitaly controlling and monitoring access to repositories by using the official gRPC + interface. +- [Gitaly Cluster](praefect.md) has optimizations, such as fault tolerance and + [distributed reads](praefect.md#distributed-reads), that depend on the gRPC interface and database + to determine repository state. + +WARNING: +Accessing Git repositories directly is done at your own risk and is not supported. ## Direct access to Git in GitLab Direct access to Git uses code in GitLab known as the "Rugged patches". -### History - -Before Gitaly existed, what are now Gitaly clients used to access Git repositories directly, either: +Before Gitaly existed, what are now Gitaly clients accessed Git repositories directly, either: -- On a local disk in the case of a single-machine Omnibus GitLab installation +- On a local disk in the case of a single-machine Omnibus GitLab installation. - Using NFS in the case of a horizontally-scaled GitLab installation. -Besides running plain `git` commands, GitLab used to use a Ruby library called +In addition to running plain `git` commands, GitLab used a Ruby library called [Rugged](https://github.com/libgit2/rugged). Rugged is a wrapper around [libgit2](https://libgit2.org/), a stand-alone implementation of Git in the form of a C library. @@ -81,9 +305,9 @@ not an external process, there was very little overhead between: - GitLab application code that tried to look up data in Git repositories. - The Git implementation itself. -Because the combination of Rugged and Unicorn was so efficient, the GitLab application code ended up with lots of -duplicate Git object lookups. For example, looking up the `master` commit a dozen times in one -request. We could write inefficient code without poor performance. +Because the combination of Rugged and Unicorn was so efficient, the GitLab application code ended up +with lots of duplicate Git object lookups. For example, looking up the default branch commit a dozen +times in one request. We could write inefficient code without poor performance. When we migrated these Git lookups to Gitaly calls, we suddenly had a much higher fixed cost per Git lookup. Even when Gitaly is able to re-use an already-running `git` process (for example, to look up @@ -94,8 +318,8 @@ a commit), you still have: Using GitLab.com to measure, we reduced the number of Gitaly calls per request until the loss of Rugged's efficiency was no longer felt. It also helped that we run Gitaly itself directly on the Git -file severs, rather than by using NFS mounts. This gave us a speed boost that counteracted the negative -effect of not using Rugged anymore. +file servers, rather than by using NFS mounts. This gave us a speed boost that counteracted the +negative effect of not using Rugged anymore. Unfortunately, other deployments of GitLab could not remove NFS like we did on GitLab.com, and they got the worst of both worlds: @@ -154,7 +378,29 @@ There are two facets to our efforts to remove direct Git access in GitLab: NFS. The second facet presents the only real solution. For this, we developed -[Gitaly Cluster](praefect.md). +[Gitaly Cluster](#gitaly-cluster). + +## NFS deprecation notice + +<!-- vale gitlab.FutureTense = NO --> + +From GitLab 14.0, enhancements and bug fixes for NFS for Git repositories will no longer be +considered and customer technical support will be considered out of scope. + +Additional information: + +- [Recommended NFS mount options and known issues with Gitaly and NFS](../nfs.md#upgrade-to-gitaly-cluster-or-disable-caching-if-experiencing-data-loss). +- [GitLab statement of support](https://about.gitlab.com/support/statement-of-support.html#gitaly-and-nfs). + +<!-- vale gitlab.FutureTense = YES --> + +GitLab recommends: + +- Creating a [Gitaly Cluster](#gitaly-cluster) as soon as possible. +- [Moving your repositories](praefect.md#migrate-to-gitaly-cluster) from NFS-based storage to Gitaly + Cluster. + +We welcome your feedback on this process: raise a support ticket, or [comment on the epic](https://gitlab.com/groups/gitlab-org/-/epics/4916). ## Troubleshooting Gitaly @@ -213,6 +459,21 @@ You can run a gRPC trace with: sudo GRPC_TRACE=all GRPC_VERBOSITY=DEBUG gitlab-rake gitlab:gitaly:check ``` +### Server side gRPC logs + +gRPC tracing can also be enabled in Gitaly itself with the `GODEBUG=http2debug` +environment variable. To set this in an Omnibus GitLab install: + +1. Add the following to your `gitlab.rb` file: + + ```ruby + gitaly['env'] = { + "GODEBUG=http2debug" => "2" + } + ``` + +1. [Reconfigure](../restart_gitlab.md#omnibus-gitlab-reconfigure) GitLab. + ### Correlating Git processes with RPCs Sometimes you need to find out which Gitaly RPC created a particular Git process. @@ -240,9 +501,9 @@ so, there's not that much visibility into what goes on inside If you have Prometheus set up to scrape your Gitaly process, you can see request rates and error codes for individual RPCs in `gitaly-ruby` by querying `grpc_client_handled_total`. Strictly speaking, this metric does -not differentiate between `gitaly-ruby` and other RPCs, but in practice -(as of GitLab 11.9), all gRPC calls made by Gitaly itself are internal -calls from the main Gitaly process to one of its `gitaly-ruby` sidecars. +not differentiate between `gitaly-ruby` and other RPCs. However from GitLab 11.9, +all gRPC calls made by Gitaly itself are internal calls from the main Gitaly process to one of its +`gitaly-ruby` sidecars. Assuming your `grpc_client_handled_total` counter observes only Gitaly, the following query shows you RPCs are (most likely) internally @@ -349,9 +610,10 @@ update the secrets file on the Gitaly server to match the Gitaly client, then ### Command line tools cannot connect to Gitaly -If you can't connect to a Gitaly server with command line (CLI) tools, -and certain actions result in a `14: Connect Failed` error message, -gRPC cannot reach your Gitaly server. +gRPC cannot reach your Gitaly server if: + +- You can't connect to a Gitaly server with command-line tools. +- Certain actions result in a `14: Connect Failed` error message. Verify you can reach Gitaly by using TCP: @@ -383,16 +645,30 @@ unset http_proxy unset https_proxy ``` -### Permission denied errors appearing in Gitaly logs when accessing repositories from a standalone Gitaly server +### Permission denied errors appearing in Gitaly or Praefect logs when accessing repositories -If this error occurs even though file permissions are correct, it's likely that -the Gitaly server is experiencing -[clock drift](https://en.wikipedia.org/wiki/Clock_drift). +You might see the following in Gitaly and Praefect logs: -Ensure the Gitaly clients and servers are synchronized, and use an NTP time -server to keep them synchronized, if possible. +```shell +{ + ... + "error":"rpc error: code = PermissionDenied desc = permission denied", + "grpc.code":"PermissionDenied", + "grpc.meta.client_name":"gitlab-web", + "grpc.request.fullMethod":"/gitaly.ServerService/ServerInfo", + "level":"warning", + "msg":"finished unary call with code PermissionDenied", + ... +} +``` -### Praefect +This is a GRPC call +[error response code](https://grpc.github.io/grpc/core/md_doc_statuscodes.html). -Praefect is a router and transaction manager for Gitaly, and a required -component for running a Gitaly Cluster. For more information see [Gitaly Cluster](praefect.md). +If this error occurs, even though +[the Gitaly auth tokens are correctly setup](../gitaly/praefect.md#debugging-praefect), +it's likely that the Gitaly servers are experiencing +[clock drift](https://en.wikipedia.org/wiki/Clock_drift). + +Ensure the Gitaly clients and servers are synchronized, and use an NTP time +server to keep them synchronized. |