Merge branch 'docs-update-ha' into 'master'

Docs update ha

See merge request !11446

doc/administration/high_availability/README.md

@@ -5,6 +5,20 @@ The solution you choose will be based on the level of scalability and
 availability you require. The easiest solutions are scalable, but not necessarily
 highly available.
 
+GitLab provides a service that is usually essential to most organizations: it
+enables people to collaborate on code in a timely fashion. Any downtime should
+therefore be short and planned. Luckily, GitLab provides a solid setup even on
+a single server without special measures. Due to the distributed nature
+of Git, developers can still commit code locally even when GitLab is not
+available. However, some GitLab features such as the issue tracker and
+Continuous Integration are not available when GitLab is down.
+
+**Keep in mind that all Highly Available solutions come with a trade-off between
+cost/complexity and uptime**. The more uptime you want, the more complex the
+solution. And the more complex the solution, the more work is involved in
+setting up and maintaining it. High availability is not free and every HA
+solution should balance the costs against the benefits.
+
 ## Architecture
 
 There are two kinds of setups:
@@ -37,6 +51,10 @@ Block Device) to keep all data in sync. DRBD requires a low latency link to
 remain in sync. It is not advisable to attempt to run DRBD between data centers
 or in different cloud availability zones.
 
+> **Note:** GitLab recommends against choosing this HA method because of the
+  complexity of managing DRBD and crafting automatic failover. This is
+  *compatible* with GitLab, but not officially *supported*.
+
 Components/Servers Required: 2 servers/virtual machines (one active/one passive)
 
 ![Active/Passive HA Diagram](../img/high_availability/active-passive-diagram.png)

doc/administration/high_availability/nfs.md

@@ -7,6 +7,25 @@ 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.
 
+## AWS Elastic File System
+
+GitLab does not recommend using AWS Elastic File System (EFS).
+
+Customers and users have reported that AWS EFS does not perform well for GitLab's
+use-case. There are several issues that can cause problems. For these reasons
+GitLab does not recommend using EFS with GitLab.
+
+- EFS bases allowed IOPS on volume size. The larger the volume, the more IOPS
+  are allocated. For smaller volumes, users may experience decent performance
+  for a period of time due to 'Burst Credits'. Over a period of weeks to months
+  credits may run out and performance will bottom out.
+- For larger volumes, allocated IOPS may not be the problem. Workloads where
+  many small files are written in a serialized manner are not well-suited for EFS.
+  EBS with an NFS server on top will perform much better.
+
+For more details on another person's experience with EFS, see
+[Amazon's Elastic File System: Burst Credits](https://www.rawkode.io/2017/04/amazons-elastic-file-system-burst-credits/)
+
 ### Recommended options
 
 When you define your NFS exports, we recommend you also add the following

doc/university/high-availability/aws/README.md

@@ -159,19 +159,21 @@ subnet and security group and
 
 ***
 
-## Elastic File System
+## Network File System
 
-This new AWS offering allows us to create a file system accessible by

-EC2 instances within a VPC. Choose our VPC and the subnets will be
-
automatically configured assuming we don't need to set explicit IPs.
-The
next section allows us to add tags and choose between General
-Purpose or
Max I/O which is a good option when being accessed by a
-large number of
EC2 instances.
+GitLab requires a shared filesystem such as NFS. The file share(s) will be
+mounted on all application servers. There are a variety of ways to build an
+NFS server on AWS.
 
-

![Elastic File System](img/elastic-file-system.png)
+One option is to use a third-party AMI that offers NFS as a service. A [search
+for 'NFS' in the AWS Marketplace](https://aws.amazon.com/marketplace/search/results?x=0&y=0&searchTerms=NFS&page=1&ref_=nav_search_box)
+shows options such as NetApp, SoftNAS and others.
 
-To actually mount and install the NFS client we'll use the User Data
-section when adding our Launch Configuration.
+Another option is to build a simple NFS server using a vanilla Linux server backed
+by AWS Elastic Block Storage (EBS).
+
+> **Note:** GitLab does not recommend using AWS Elastic File System (EFS). See
+  details in [High Availability NFS documentation](../../../administration/high_availability/nfs.md#aws-elastic-file-system)
 
 ***