mirror of https://github.com/status-im/consul.git
91 lines
4.4 KiB
Markdown
91 lines
4.4 KiB
Markdown
---
|
|
layout: "docs"
|
|
page_title: "Frequently Asked Questions"
|
|
sidebar_current: "docs-faq"
|
|
---
|
|
|
|
# Frequently Asked Questions
|
|
|
|
## 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://www.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.
|
|
|
|
## Q: Are _failed_ or _left_ nodes ever removed?
|
|
|
|
To prevent an accumulation of dead nodes (nodes in either _failed_ or _left_
|
|
states), Consul will automatically remove dead nodes out of the catalog. This
|
|
process is called _reaping_. This is currently done on a configurable
|
|
interval of 72 hours. Reaping is similar to leaving, causing all associated
|
|
services to be deregistered. Changing the reap interval for aesthetic
|
|
reasons to trim the number of _failed_ or _left_ nodes is not advised (nodes
|
|
in the _failed_ or _left_ state do not cause any additional burden on
|
|
Consul).
|
|
|
|
## Q: Does Consul support delta updates for watchers or blocking queries?
|
|
|
|
Consul does not currently support sending a delta or a change only response
|
|
to a watcher or a blocking query. The API simply allows for an edge-trigger
|
|
return with the full result. A client should keep the results of their last
|
|
read and compute the delta client side.
|
|
|
|
By design, Consul offloads this to clients instead of attempting to support
|
|
the delta calculation. This avoids expensive state maintenance on the servers
|
|
as well as race conditions between data updates and watch registrations.
|
|
|
|
## Q: What network ports does Consul use?
|
|
|
|
Consul agents communicate on the following TCP and UDP ports:
|
|
|
|
| Port | Protocol | Description |
|
|
| ------ | --------- | ----------------------------------------------------|
|
|
| 8300 | TCP | RPC for client/server and server/server replication |
|
|
| 8301 | TCP & UDP | LAN gossip from client/client and client/server |
|
|
| 8302 | TCP | WAN gossip from server/server |
|