open-consul/website/source/api/kv.html.md

layout	page_title	sidebar_current	description
api	KV Store - HTTP API	api-kv-store	The /kv endpoints access Consul's simple key/value store, useful for storing service configuration or other metadata.

KV Store Endpoints

The /kv endpoints access Consul's simple key/value store, useful for storing service configuration or other metadata.

It is important to note that each datacenter has its own KV store, and there is no built-in replication between datacenters. If you are interested in replication between datacenters, please view the Consul Replicate project.

~> Values in the KV store cannot be larger than 512kb.

For multi-key updates, please consider using transaction.

Read Key

This endpoint returns the specified key. If no key exists at the given path, a 404 is returned instead of a 200 response.

For multi-key reads, please consider using transaction.

Method	Path	Produces
GET	/kv/:key	application/json

The table below shows this endpoint's support for blocking queries, consistency modes, agent caching, and required ACLs.

Blocking Queries	Consistency Modes	Agent Caching	ACL Required
YES	all	none	key:read

Parameters

• key (string: "") - Specifies the path of the key to read.

• dc (string: "") - Specifies the datacenter to query. This will default to the datacenter of the agent being queried. This is specified as part of the URL as a query parameter.

• recurse (bool: false) - Specifies if the lookup should be recursive and key treated as a prefix instead of a literal match. This is specified as part of the URL as a query parameter.

• raw (bool: false) - Specifies the response is just the raw value of the key, without any encoding or metadata. This is specified as part of the URL as a query parameter.

• keys (bool: false) - Specifies to return only keys (no values or metadata). Specifying this implies recurse. This is specified as part of the URL as a query parameter.

• separator (string: '') - Specifies the string to use as a separator for recursive key lookups. This option is only used when paired with the keys parameter to limit the prefix of keys returned, only up to the given separator. This is specified as part of the URL as a query parameter.

Sample Request

$ curl \
    http://127.0.0.1:8500/v1/kv/my-key

Sample Response

Metadata Response

[
  {
    "CreateIndex": 100,
    "ModifyIndex": 200,
    "LockIndex": 200,
    "Key": "zip",
    "Flags": 0,
    "Value": "dGVzdA==",
    "Session": "adf4238a-882b-9ddc-4a9d-5b6758e4159e"
  }
]

• CreateIndex is the internal index value that represents when the entry was created.

• ModifyIndex is the last index that modified this key. This index corresponds to the X-Consul-Index header value that is returned in responses, and it can be used to establish blocking queries by setting the ?index query parameter. You can even perform blocking queries against entire subtrees of the KV store: if ?recurse is provided, the returned X-Consul-Index corresponds to the latest ModifyIndex within the prefix, and a blocking query using that ?index will wait until any key within that prefix is updated.

• LockIndex is the number of times this key has successfully been acquired in a lock. If the lock is held, the Session key provides the session that owns the lock.

• Key is simply the full path of the entry.

• Flags is an opaque unsigned integer that can be attached to each entry. Clients can choose to use this however makes sense for their application.

• Value is a base64-encoded blob of data.

Keys Response

When using the ?keys query parameter, the response structure changes to an array of strings instead of an array of JSON objects. Listing /web/ with a / separator may return:

[
  "/web/bar",
  "/web/foo",
  "/web/subdir/"
]

Using the key listing method may be suitable when you do not need the values or flags or want to implement a key-space explorer.

Raw Response

When using the ?raw endpoint, the response is not application/json, but rather the content type of the uploaded content.

)k<><6B><EFBFBD><EFBFBD><EFBFBD><EFBFBD>z^<5E>-<2D>ɑj<C991>q<EFBFBD><71><EFBFBD><EFBFBD>#u<>-R<>r<EFBFBD><72>T<EFBFBD>D<EFBFBD><44>٬<EFBFBD>Y<EFBFBD><59>l,<2C>ιK<CEB9><4B>Fm<46><6D>}<7D>#e<><65>

(Yes, that is intentionally a bunch of gibberish characters to showcase the response)

Create/Update Key

This endpoint

Method	Path	Produces
PUT	/kv/:key	application/json

Even though the return type is application/json, the value is either true or false, indicating whether the create/update succeeded.

The table below shows this endpoint's support for blocking queries, consistency modes, agent caching, and required ACLs.

Blocking Queries	Consistency Modes	Agent Caching	ACL Required
NO	none	none	key:write

Parameters

• key (string: "") - Specifies the path of the key to read.

• dc (string: "") - Specifies the datacenter to query. This will default to the datacenter of the agent being queried. This is specified as part of the URL as a query parameter.

• flags (int: 0) - Specifies an unsigned value between 0 and (2^64)-1. Clients can choose to use this however makes sense for their application. This is specified as part of the URL as a query parameter.

• cas (int: 0) - Specifies to use a Check-And-Set operation. This is very useful as a building block for more complex synchronization primitives. If the index is 0, Consul will only put the key if it does not already exist. If the index is non-zero, the key is only set if the index matches the ModifyIndex of that key.

• acquire (string: "") - Supply a session ID to use in a lock acquisition operation. This is useful as it allows leader election to be built on top of Consul. If the lock is not held and the session is valid, this increments the LockIndex and sets the Session value of the key in addition to updating the key contents. A key does not need to exist to be acquired. If the lock is already held by the given session, then the LockIndex is not incremented but the key contents are updated. This lets the current lock holder update the key contents without having to give up the lock and reacquire it. Note that an update that does not include the acquire parameter will proceed normally even if another session has locked the key.

  For an example of how to use the lock feature, see the [Leader Election Guide] (https://learn.hashicorp.com/consul/developer-configuration/elections).

• release (string: "") - Supply a session ID to use in a release operation. This is useful when paired with ?acquire= as it allows clients to yield a lock. This will leave the LockIndex unmodified but will clear the associated Session of the key. The key must be held by this session to be unlocked.

Sample Payload

The payload is arbitrary, and is loaded directly into Consul as supplied.

Sample Requests

$ curl \
    --request PUT \
    --data @contents \
    http://127.0.0.1:8500/v1/kv/my-key

# or

$ curl \
    --request PUT \
    --data-binary @contents \
    http://127.0.0.1:8500/v1/kv/my-key

Sample Response

true

Delete Key

This endpoint deletes a single key or all keys sharing a prefix.

Method	Path	Produces
DELETE	/kv/:key	application/json

The table below shows this endpoint's support for blocking queries, consistency modes, agent caching, and required ACLs.

Blocking Queries	Consistency Modes	Agent Caching	ACL Required
NO	none	none	key:write

Parameters

• recurse (bool: false) - Specifies to delete all keys which have the specified prefix. Without this, only a key with an exact match will be deleted.

• cas (int: 0) - Specifies to use a Check-And-Set operation. This is very useful as a building block for more complex synchronization primitives. Unlike PUT, the index must be greater than 0 for Consul to take any action: a 0 index will not delete the key. If the index is non-zero, the key is only deleted if the index matches the ModifyIndex of that key.

Sample Request

$ curl \
    --request DELETE \
    http://127.0.0.1:8500/v1/kv/my-key

Sample Response

true