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