mirror of https://github.com/status-im/consul.git
100 lines
4.8 KiB
Plaintext
100 lines
4.8 KiB
Plaintext
---
|
||
layout: docs
|
||
page_title: Consul KV
|
||
sidebar_title: Consul KV
|
||
description: Consul KV is a core feature of Consul and is installed with the Consul agent.
|
||
---
|
||
|
||
# Consul KV
|
||
|
||
Consul KV is a core feature of Consul and is installed with the Consul agent.
|
||
Once installed with the agent, it will have sane defaults. Consul KV allows
|
||
users to store indexed objects, though its main uses are storing configuration
|
||
parameters and metadata. Please note that it is a simple KV store and is not
|
||
intended to be a full featured datastore (such as DynamoDB) but has some
|
||
similarities to one.
|
||
|
||
The Consul KV datastore is located on the servers, but can be accessed by any
|
||
agent (client or server). The natively integrated [RPC
|
||
functionality](/docs/internals/architecture) allows clients to forward
|
||
requests to servers, including key/value reads and writes. Part of Consul’s
|
||
core design allows data to be replicated automatically across all the servers.
|
||
Having a quorum of servers will decrease the risk of data loss if an outage
|
||
occurs.
|
||
|
||
If you have not used Consul KV, check out this [Getting Started
|
||
tutorial](https://learn.hashicorp.com/tutorials/consul/get-started-key-value-store?utm_source=consul.io&utm_medium=docs) on HashiCorp
|
||
Learn.
|
||
|
||
## Accessing the KV store
|
||
|
||
The KV store can be accessed by the [consul kv CLI
|
||
subcommands](/commands/kv), [HTTP API](/api/kv), and Consul UI.
|
||
To restrict access, enable and configure
|
||
[ACLs](https://learn.hashicorp.com/tutorials/consul/access-control-setup-production).
|
||
Once the ACL system has been bootstrapped, users and services, will need a
|
||
valid token with KV [privileges](/docs/agent/acl-rules#key-value-rules) to
|
||
access the the data store, this includes even reads. We recommend creating a
|
||
token with limited privileges, for example, you could create a token with write
|
||
privileges on one key for developers to update the value related to their
|
||
application.
|
||
|
||
The datastore itself is located on the Consul servers in the [data
|
||
directory](/docs/agent/options#_data_dir). To ensure data is not lost in
|
||
the event of a complete outage, use the [`consul snapshot`](/commands/snapshot/restore) feature to backup the data.
|
||
|
||
## Using Consul KV
|
||
|
||
Objects are opaque to Consul, meaning there are no restrictions on the type of
|
||
object stored in a key/value entry. The main restriction on an object is size -
|
||
the maximum is 512 KB. Due to the maximum object size and main use cases, you
|
||
should not need extra storage; the general [sizing
|
||
recommendations](/docs/agent/options#kv_max_value_size)
|
||
are usually sufficient.
|
||
|
||
Keys, like objects are not restricted by type and can include any character.
|
||
However, we recommend using URL-safe chars - `[a-zA-Z0-9-._~]` with the
|
||
exception of `/`, which can be used to help organize data. Note, `/` will be
|
||
treated like any other character and is not fixed to the file system. Meaning,
|
||
including `/` in a key does not fix it to a directory structure. This model is
|
||
similar to Amazon S3 buckets. However, `/` is still useful for organizing data
|
||
and when recursively searching within the data store. We also recommend that
|
||
you avoid the use of `*`, `?`, `'`, and `%` because they can cause issues when
|
||
using the API and in shell scripts.
|
||
|
||
## Extending Consul KV
|
||
|
||
### Consul Template
|
||
|
||
If you plan to use Consul KV as part of your configuration management process
|
||
review the [Consul
|
||
Template](https://learn.hashicorp.com/tutorials/consul/consul-template)
|
||
tutorial on how to update configuration based on value updates in the KV. Consul
|
||
Template is based on Go Templates and allows for a series of scripted actions
|
||
to be initiated on value changes to a Consul key.
|
||
|
||
### Watches
|
||
|
||
Consul KV can also be extended with the use of watches.
|
||
[Watches](/docs/agent/watches) are a way to monitor data for updates. When
|
||
an update is detected, an external handler is invoked. To use watches with the
|
||
KV store the [key](/docs/agent/watches#key) watch type should be used.
|
||
|
||
### Consul Sessions
|
||
|
||
Consul sessions can be used to build distributed locks with Consul KV. Sessions
|
||
act as a binding layer between nodes, health checks, and key/value data. The KV
|
||
API supports an `acquire` and `release` operation. The `acquire` operation acts
|
||
like a Check-And-Set operation. On success, there is a key update and an
|
||
increment to the `LockIndex` and the session value is updated to reflect the
|
||
session holding the lock. Review the session documentation for more information
|
||
on the [integration](/docs/internals/sessions#k-v-integration).
|
||
|
||
Review the following tutorials to learn how to use Consul sessions for [application leader election](https://learn.hashicorp.com/tutorials/consul/application-leader-elections) and
|
||
to [build distributed semaphores](https://learn.hashicorp.com/tutorials/consul/distributed-semaphore).
|
||
|
||
### Vault
|
||
|
||
If you plan to use Consul KV as a backend for Vault, please review [this
|
||
tutorial](https://learn.hashicorp.com/tutorials/vault/ha-with-consul).
|