mirror of https://github.com/status-im/consul.git
70 lines
3.3 KiB
Markdown
70 lines
3.3 KiB
Markdown
---
|
|
layout: "docs"
|
|
page_title: "Frequently Asked Questions"
|
|
sidebar_current: "docs-faq"
|
|
---
|
|
|
|
# Frequently Asked Questions
|
|
|
|
## Q: Why is virtual memory usage high?
|
|
|
|
Consul makes use of [LMDB](http://symas.com/mdb/) internally for various data
|
|
storage purposes. LMDB relies on using memory-mapping, a technique in which
|
|
a sparse file is represented as a contiguous range of memory. Consul configures
|
|
high limits for these file sizes and as a result relies on large chunks of
|
|
virtual memory to be allocated. However, in practice, the limits are much larger
|
|
than any realistic deployment of Consul would ever use, and the resident memory or
|
|
physical memory used is much lower.
|
|
|
|
## Q: What is Checkpoint? / Does Consul call home?
|
|
|
|
Consul makes use of a HashiCorp service called [Checkpoint](http://checkpoint.hashicorp.com)
|
|
which is used to check for updates and critical security bulletins.
|
|
Only anonymous information, which cannot be used to identify the user or host, is
|
|
sent to Checkpoint . An anonymous ID is sent which helps de-duplicate warning messages.
|
|
This anonymous ID can can be disabled. In fact, using the Checkpoint service is optional
|
|
and can be disabled.
|
|
|
|
See [`disable_anonymous_signature`](/docs/agent/options.html#disable_anonymous_signature)
|
|
and [`disable_update_check`](/docs/agent/options.html#disable_update_check).
|
|
|
|
## Q: How does Atlas integration work?
|
|
|
|
Consul makes use of a HashiCorp service called [SCADA](http://scada.hashicorp.com)
|
|
(Supervisory Control And Data Acquisition). The SCADA system allows clients to maintain
|
|
long-running connections to Atlas. Atlas can in turn provide auto-join facilities for
|
|
Consul agents (supervisory control) and an integrated dashboard showing the health of
|
|
all connected agents (data acquisition).
|
|
|
|
Standard ACLs can be applied to the SCADA connection, ensuring that Atlas is given only
|
|
those privileges that make sense for your deployment.
|
|
|
|
Using the SCADA service is optional. SCADA is only enabled by opt-in.
|
|
|
|
See the [Atlas integration guide](/docs/guides/atlas.html) for more details.
|
|
|
|
## Q: Does Consul rely on UDP Broadcast or Multicast?
|
|
|
|
Consul uses the [Serf](https://serfdom.io) gossip protocol which relies on
|
|
TCP and UDP unicast. Broadcast and Multicast are rarely available in a multi-tenant
|
|
or cloud network environment. For that reason, Consul and Serf were both
|
|
designed to avoid any dependence on those capabilities.
|
|
|
|
## Q: Is Consul eventually or strongly consistent?
|
|
|
|
Consul has two important subsystems, the service catalog and the gossip protocol.
|
|
The service catalog stores all the nodes, service instances, health check data,
|
|
ACLs, and Key/Value information. It is strongly consistent, and replicated
|
|
using the [consensus protocol](/docs/internals/consensus.html).
|
|
|
|
The [gossip protocol](/docs/internals/gossip.html) is used to track which
|
|
nodes are part of the cluster and to detect a node or agent failure. This information
|
|
is eventually consistent by nature. When the servers detects a change in membership,
|
|
or receive a health update, they update the service catalog appropriately.
|
|
|
|
Because of this split, the answer to the question is subtle. Almost all client APIs
|
|
interact with the service catalog and are strongly consistent. Updates to the
|
|
catalog may come via the gossip protocol which is eventually consistent, meaning
|
|
the current state of the catalog can lag behind until the state is reconciled.
|
|
|