130 lines
6.7 KiB
Markdown
130 lines
6.7 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 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?
|
|
|
|
Hosted Consul Enterprise in Atlas was officially deprecated on March 7th,
|
|
2017.
|
|
|
|
There are strong alternatives available and they are listed below.
|
|
|
|
For users on supported cloud platform the
|
|
[-retry-join](/docs/agent/options.html#_retry_join) option allows bootstrapping
|
|
by automatically discovering instances with a given tag key/value at startup.
|
|
|
|
For users on other cloud platforms [-join and retry-join
|
|
functionality](/docs/agent/options.html#_join) can be used to join clusters by
|
|
ip address or hostname.
|
|
|
|
Other features of Consul Enterprise, such as the UI and Alerts also have
|
|
suitable open source alternatives.
|
|
|
|
For replacing the UI, we recommend the [free UI packaged as part of Consul open source](https://www.consul.io/docs/agent/options.html#_ui). A live demo can be access at [https://demo.consul.io/ui/](https://demo.consul.io/ui/).
|
|
|
|
For replacing alerts, we recommend the [open source Consul alerts daemon](https://github.com/acalephstorage/consul-alerts). This is not maintained or supported by HashiCorp, however there is active development from the community.
|
|
|
|
## Q: Does Consul rely on UDP Broadcast or Multicast?
|
|
|
|
Consul uses the [Serf](https://www.serf.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 KV 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?
|
|
|
|
The [Ports Used](https://www.consul.io/docs/agent/options.html#ports) section of the Configuration documentation lists all ports that Consul uses.
|
|
|
|
## Q: Does Consul require certain user process resource limits?
|
|
|
|
There should be only a small number of open file descriptors required for a
|
|
Consul client agent. The gossip layers perform transient connections with
|
|
other nodes, each connection to the client agent (such as for a blocking
|
|
query) will open a connection, and there will typically be connections to one
|
|
of the Consul servers. A small number of file descriptors are also required
|
|
for watch handlers, health checks, log files, and so on.
|
|
|
|
For a Consul server agent, you should plan on the above requirements and
|
|
an additional incoming connection from each of the nodes in the cluster. This
|
|
should not be the common case, but in the worst case if there is a problem
|
|
with the other servers you would expect the other client agents to all
|
|
connect to a single server and so preparation for this possibility is helpful.
|
|
|
|
The default ulimits are usually sufficient for Consul, but you should closely
|
|
scrutinize your own environment's specific needs and identify the root cause
|
|
of any excessive resource utilization before arbitrarily increasing the limits.
|
|
|
|
## Q: What is the per-key value size limitation for Consul's key/value store?
|
|
|
|
The limit on a key's value size is 512KB. This is strictly enforced and an
|
|
HTTP 413 status will be returned to any client that attempts to store more
|
|
than that limit in a value. It should be noted that the Consul key/value store
|
|
is not designed to be used as a general purpose database. See
|
|
[Server Performance](/docs/guides/performance.html) for more details.
|
|
|
|
## Q: What data is replicated between Consul datacenters?
|
|
|
|
In general, data is not replicated between different Consul datacenters. When a
|
|
request is made for a resource in another datacenter, the local Consul servers forward
|
|
an RPC request to the remote Consul servers for that resource and return the results.
|
|
If the remote datacenter is not available, then those resources will also not be
|
|
available, but that won't otherwise affect the local datacenter. There are some special
|
|
situations where a limited subset of data can be replicated, such as with Consul's built-in
|
|
[ACL replication](/docs/guides/acl.html#outages-and-acl-replication) capability, or
|
|
external tools like [consul-replicate](https://github.com/hashicorp/consul-replicate).
|