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website/pages/docs/faq.mdx
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@ -10,10 +10,11 @@ sidebar_title: FAQ
Consul makes use of a HashiCorp service called [Checkpoint](http://checkpoint.hashicorp.com) Consul makes use of a HashiCorp service called [Checkpoint](http://checkpoint.hashicorp.com)
which is used to check for updates and critical security bulletins. 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 Only anonymous information, which cannot be used to identify the user or host,
sent to Checkpoint . An anonymous ID is sent which helps de-duplicate warning messages. is sent to Checkpoint. An anonymous ID is sent which helps de-duplicate warning
This anonymous ID can be disabled. In fact, using the Checkpoint service is optional messages.
and can be disabled. 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#disable_anonymous_signature) See [`disable_anonymous_signature`](/docs/agent/options#disable_anonymous_signature)
and [`disable_update_check`](/docs/agent/options#disable_update_check). and [`disable_update_check`](/docs/agent/options#disable_update_check).
@ -21,26 +22,29 @@ and [`disable_update_check`](/docs/agent/options#disable_update_check).
## Q: Does Consul rely on UDP Broadcast or Multicast? ## Q: Does Consul rely on UDP Broadcast or Multicast?
Consul uses the [Serf](https://www.serf.io) gossip protocol which relies on 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 TCP and UDP unicast. Broadcast and Multicast are rarely available in a
or cloud network environment. For that reason, Consul and Serf were both multi-tenant or cloud network environment. For that reason, Consul and Serf
designed to avoid any dependence on those capabilities. were both designed to avoid any dependence on those capabilities.
## Q: Is Consul eventually or strongly consistent? ## Q: Is Consul eventually or strongly consistent?
Consul has two important subsystems, the service catalog and the gossip protocol. Consul has two important subsystems, the service catalog and the gossip
protocol.
The service catalog stores all the nodes, service instances, health check data, The service catalog stores all the nodes, service instances, health check data,
ACLs, and KV information. It is strongly consistent, and replicated ACLs, and KV information. It is strongly consistent, and replicated
using the [consensus protocol](/docs/internals/consensus). using the [consensus protocol](/docs/internals/consensus).
The [gossip protocol](/docs/internals/gossip) is used to track which The [gossip protocol](/docs/internals/gossip) is used to track which
nodes are part of the cluster and to detect a node or agent failure. This information nodes are part of the cluster and to detect a node or agent failure. This
is eventually consistent by nature. When the servers detects a change in membership, information is eventually consistent by nature. When the servers detects a
or receive a health update, they update the service catalog appropriately. 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 Because of this split, the answer to the question is subtle. Almost all client
interact with the service catalog and are strongly consistent. Updates to the APIs interact with the service catalog and are strongly consistent. Updates to
catalog may come via the gossip protocol which is eventually consistent, meaning the catalog may come via the gossip protocol which is eventually consistent
the current state of the catalog can lag behind until the state is reconciled. meaning the current state of the catalog can lag behind until the state is
reconciled.
## Q: Are _failed_ or _left_ nodes ever removed? ## Q: Are _failed_ or _left_ nodes ever removed?
@ -66,7 +70,8 @@ as well as race conditions between data updates and watch registrations.
## Q: What network ports does Consul use? ## Q: What network ports does Consul use?
The [Ports Used](/docs/agent/options#ports) section of the Configuration documentation lists all ports that Consul uses. The [Ports Used](/docs/agent/options#ports) section of the Configuration
documentation lists all ports that Consul uses.
## Q: Does Consul require certain user process resource limits? ## Q: Does Consul require certain user process resource limits?
@ -98,23 +103,35 @@ is not designed to be used as a general purpose database. See
## Q: What data is replicated between Consul datacenters? ## Q: What data is replicated between Consul datacenters?
In general, data is not replicated between different Consul datacenters. When a 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 request is made for a resource in another datacenter, the local Consul servers
an RPC request to the remote Consul servers for that resource and return the results. 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 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 available from that datacenter. That will not affect the requests to the local
situations where a limited subset of data can be replicated, such as with Consul's built-in datacenter. There are some special situations where a limited subset of data
[ACL replication](https://learn.hashicorp.com/consul/day-2-operations/acl-replication) capability, or can be replicated, such as with Consul's built-in
external tools like [consul-replicate](https://github.com/hashicorp/consul-replicate). [ACL replication](https://learn.hashicorp.com/consul/day-2-operations/acl-replication)
capability, or external tools like
[consul-replicate](https://github.com/hashicorp/consul-replicate).
## Q: Can Consul natively handle protecting against other processes accessing Consul's memory state? ## Q: Can Consul natively handle protecting against other processes accessing Consul's memory state?
Consul does not provide built-in memory access protections, and doesn't interact with the host system to change or manipulate Consul does not provide built-in memory access protections, and doesn't
interact with the host system to change or manipulate
viewing and doesn't interact with the host system to change or manipulate viewing and doesn't interact with the host system to change or manipulate
application security. application security.
We recommend taking any precautions or We recommend taking any precautions or remediation steps that you would
remediation steps that you would normally do for individual processes, based normally do for individual processes, based on your operating system.
on your operating system.
Please see our Please see our
[Security Model](/docs/internals/security) for more information. [Security Model](/docs/internals/security) for more information.
## Q: Are the Consul Docker Images OCI Compliant?
The official [Consul Docker image](https://hub.docker.com/_/consul/) uses
[Docker image schema](https://docs.docker.com/registry/spec/manifest-v2-2/) V2,
which is OCI Compliant. To check the docker images on Docker Hub, use the
command `docker manifest inspect consul` to inspect the manifest payload. The
`docker manifest inspect` may require you to enable experimental features to
use.