58 lines
3.1 KiB
Markdown
58 lines
3.1 KiB
Markdown
---
|
|
layout: "intro"
|
|
page_title: "Consul vs. SmartStack"
|
|
sidebar_current: "vs-other-smartstack"
|
|
---
|
|
|
|
# Consul vs. SmartStack
|
|
|
|
SmartStack is another tool which tackles the service discovery problem.
|
|
It has a rather unique architecture, and has 4 major components: ZooKeeper,
|
|
HAProxy, Synapse, and Nerve. The ZooKeeper servers are responsible for storing cluster
|
|
state in a consistent and fault tolerant manner. Each node in the SmartStack
|
|
cluster then runs both Nerves and Synapses. The Nerve is responsible for running
|
|
health checks against a service, and registering with the ZooKeeper servers.
|
|
Synapse queries ZooKeeper for service providers and dynamically configures
|
|
HAProxy. Finally, clients speak to HAProxy, which does health checking and
|
|
load balancing across service providers.
|
|
|
|
Consul is a much simpler and more contained system, as it does not rely on any external
|
|
components. Consul uses an integrated [gossip protocol](/docs/internals/gossip.html)
|
|
to track all nodes and perform server discovery. This means that server addresses
|
|
do not need to be hardcoded and updated fleet wide on changes, unlike SmartStack.
|
|
|
|
Service registration for both Consul and Nerves can be done with a configuration file,
|
|
but Consul also supports an API to dynamically change the services and checks that are in use.
|
|
|
|
For discovery, SmartStack clients must use HAProxy, requiring that Synapse be
|
|
configured with all desired endpoints in advance. Consul clients instead
|
|
use the DNS or HTTP APIs without any configuration needed in advance. Consul
|
|
also provides a "tag" abstraction, allowing services to provide metadata such
|
|
as versions, primary/secondary designations, or opaque labels that can be used for
|
|
filtering. Clients can then request only the service providers which have
|
|
matching tags.
|
|
|
|
The systems also differ in how they manage health checking.
|
|
Nerve's performs local health checks in a manner similar to Consul agents.
|
|
However, Consul maintains seperate catalog and health systems, which allow
|
|
operators to see which nodes are in each service pool, as well as providing
|
|
insight into failing checks. Nerve simply deregisters nodes on failed checks,
|
|
providing limited operator insight. Synapse also configures HAProxy to perform
|
|
additional health checks. This causes all potential service clients to check for
|
|
liveness. With large fleets, this N-to-N style health checking may be prohibitively
|
|
expensive.
|
|
|
|
Consul generally provides a much richer health checking system. Consul supports
|
|
Nagios style plugins, enabling a vast catalog of checks to be used. It also
|
|
allows for service and host-level checks. There is also a "dead man's switch"
|
|
check that allows applications to easily integrate custom health checks. All of this
|
|
is also integrated into a Health and Catalog system with APIs enabling operator
|
|
to gain insight into the broader system.
|
|
|
|
In addition to the service discovery and health checking, Consul also provides
|
|
an integrated key/value store for configuration and multi-datacenter support.
|
|
While it may be possible to configure SmartStack for multiple datacenters,
|
|
the central ZooKeeper cluster would be a serious impediment to a fault tolerant
|
|
deployment.
|
|
|