mirror of https://github.com/hashicorp/consul
87 lines
4.2 KiB
Markdown
87 lines
4.2 KiB
Markdown
---
|
|
layout: "docs"
|
|
page_title: "Server Performance"
|
|
sidebar_current: "docs-guides-performance"
|
|
description: |-
|
|
Consul requires different amounts of compute resources, depending on cluster size and expected workload. This guide provides guidance on choosing compute resources.
|
|
---
|
|
|
|
# Server Performance
|
|
|
|
Since Consul servers run a [consensus protocol](/docs/internals/consensus.html) to
|
|
process all write operations and are contacted on nearly all read operations, server
|
|
performance is critical for overall throughput and health of a Consul cluster. Servers
|
|
are generally I/O bound for writes because the underlying Raft log store performs a sync
|
|
to disk every time an entry is appended. Servers are generally CPU bound for reads since
|
|
reads work from a fully in-memory data store that is optimized for concurrent access.
|
|
|
|
<a name="minimum"></a>
|
|
## Minimum Server Requirements
|
|
|
|
In Consul 0.7, the default server [performance parameters](/docs/agent/options.html#performance)
|
|
were tuned to allow Consul to run reliably (but relatively slowly) on a server cluster of three
|
|
[AWS t2.micro](https://aws.amazon.com/ec2/instance-types/) instances. These thresholds
|
|
were determined empirically using a leader instance that was under sufficient read, write,
|
|
and network load to cause it to permanently be at zero CPU credits, forcing it to the baseline
|
|
performance mode for that instance type. Real-world workloads typically have more bursts of
|
|
activity, so this is a conservative and pessimistic tuning strategy.
|
|
|
|
This default was chosen based on feedback from users, many of whom wanted a low cost way
|
|
to run small production or development clusters with low cost compute resources, at the
|
|
expense of some performance in leader failure detection and leader election times.
|
|
|
|
The default performance configuration is equivalent to this:
|
|
|
|
```javascript
|
|
{
|
|
"performance": {
|
|
"raft_multiplier": 5
|
|
}
|
|
}
|
|
```
|
|
|
|
<a name="production"></a>
|
|
## Production Server Requirements
|
|
|
|
When running Consul 0.7 and later in production, it is recommended to configure the server
|
|
[performance parameters](/docs/agent/options.html#performance) back to Consul's original
|
|
high-performance settings. This will let Consul servers detect a failed leader and complete
|
|
leader elections much more quickly than the default configuration which extends key Raft
|
|
timeouts by a factor of 5, so it quite slow during these events.
|
|
|
|
The high performance configuration is simple and looks like this:
|
|
|
|
```javascript
|
|
{
|
|
"performance": {
|
|
"raft_multiplier": 1
|
|
}
|
|
}
|
|
```
|
|
|
|
It's best to benchmark with a realistic workload when choosing a production server for Consul.
|
|
Here are some general recommendations:
|
|
|
|
* For write-heavy workloads, disk speed on the servers is key for performance. Use SSDs or
|
|
another fast disk technology for the best write throughput.
|
|
|
|
* <a name="last-contact"></a>Spurious leader elections can be caused by networking issues between
|
|
the servers or insufficient CPU resources. Users in cloud environments often bump their servers
|
|
up to the next instance class with improved networking and CPU until leader elections stabilize,
|
|
and in Consul 0.7 or later the [performance parameters](/docs/agent/options.html#performance)
|
|
configuration now gives you tools to trade off performance instead of upsizing servers. You can
|
|
use the [`consul.raft.leader.lastContact` telemetry](/docs/agent/telemetry.html#last-contact)
|
|
to observe how the Raft timing is performing and guide the decision to de-tune Raft performance
|
|
or add more powerful servers.
|
|
|
|
* For DNS-heavy workloads, configuring all Consul agents in a cluster with the
|
|
[`allow_stale`](/docs/agent/options.html#allow_stale) configuration option will allow reads to
|
|
scale across all Consul servers, not just the leader. See [Stale Reads](/docs/guides/dns-cache.html#stale)
|
|
in the [DNS Caching](/docs/guides/dns-cache.html) guide for more details. It's also good to set
|
|
reasonable, non-zero [DNS TTL values](/docs/guides/dns-cache.html#ttl) if your clients will
|
|
respect them.
|
|
|
|
* In other applications that perform high volumes of reads against Consul, consider using the
|
|
[stale consistency mode](/docs/agent/http.html#consistency) available to allow reads to scale
|
|
across all the servers and not just be forwarded to the leader.
|