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| layout | page_title | sidebar_current | description |
|---|---|---|---|
| intro | Key/Value Data | gettingstarted-kv | In addition to providing service discovery and integrated health checking, Consul provides an easy to use Key/Value store. This can be used to hold dynamic configuration, assist in service coordination, build leader election, and enable anything else a developer can think to build. |
Key/Value Data
In addition to providing service discovery and integrated health checking, Consul provides an easy to use Key/Value store. This can be used to hold dynamic configuration, assist in service coordination, build leader election, and enable anything else a developer can think to build.
This step assumes you have at least one Consul agent already running.
Simple Usage
To demonstrate how simple it is to get started, we will manipulate a few keys in the K/V store.
Querying the local agent we started in the Run the Agent step, we can first verify that there are no existing keys in the k/v store:
$ curl -v http://localhost:8500/v1/kv/?recurse
* About to connect() to localhost port 8500 (#0)
* Trying 127.0.0.1... connected
> GET /v1/kv/?recurse HTTP/1.1
> User-Agent: curl/7.22.0 (x86_64-pc-linux-gnu) libcurl/7.22.0 OpenSSL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
> Host: localhost:8500
> Accept: */*
>
< HTTP/1.1 404 Not Found
< X-Consul-Index: 1
< Date: Fri, 11 Apr 2014 02:10:28 GMT
< Content-Length: 0
< Content-Type: text/plain; charset=utf-8
<
* Connection #0 to host localhost left intact
* Closing connection #0
Since there are no keys, we get a 404 response back. Now, we can PUT a
few example keys:
$ curl -X PUT -d 'test' http://localhost:8500/v1/kv/web/key1
true
$ curl -X PUT -d 'test' http://localhost:8500/v1/kv/web/key2?flags=42
true
$ curl -X PUT -d 'test' http://localhost:8500/v1/kv/web/sub/key3
true
$ curl http://localhost:8500/v1/kv/?recurse
[{"CreateIndex":97,"ModifyIndex":97,"Key":"web/key1","Flags":0,"Value":"dGVzdA=="},
{"CreateIndex":98,"ModifyIndex":98,"Key":"web/key2","Flags":42,"Value":"dGVzdA=="},
{"CreateIndex":99,"ModifyIndex":99,"Key":"web/sub/key3","Flags":0,"Value":"dGVzdA=="}]
Here we have created 3 keys, each with the value of "test". Note that the
Value field returned is base64 encoded to allow non-UTF8 characters. For the
key "web/key2", we set a flag value of 42. All keys support setting a 64-bit
integer flag value. This is not used internally by Consul, but it can be used by
clients to add meaningful metadata to any KV.
After setting the values, we then issued a GET request to retrieve multiple
keys using the ?recurse parameter.
You can also fetch a single key just as easily:
$ curl http://localhost:8500/v1/kv/web/key1
[{"CreateIndex":97,"ModifyIndex":97,"Key":"web/key1","Flags":0,"Value":"dGVzdA=="}]
Deleting keys is simple as well, accomplished by using the DELETE verb. We can
delete a single key by specifying the full path, or we can recursively delete all
keys under a root using "?recurse":
$ curl -X DELETE http://localhost:8500/v1/kv/web/sub?recurse
$ curl http://localhost:8500/v1/kv/web?recurse
[{"CreateIndex":97,"ModifyIndex":97,"Key":"web/key1","Flags":0,"Value":"dGVzdA=="},
{"CreateIndex":98,"ModifyIndex":98,"Key":"web/key2","Flags":42,"Value":"dGVzdA=="}]
A key can be modified by issuing a PUT request to the same URI and
providing a different message body. Additionally, Consul provides a
Check-And-Set operation, enabling atomic key updates. This is done by
providing the ?cas= parameter with the last ModifyIndex value from
the GET request. For example, suppose we wanted to update "web/key1":
$ curl -X PUT -d 'newval' http://localhost:8500/v1/kv/web/key1?cas=97
true
$ curl -X PUT -d 'newval' http://localhost:8500/v1/kv/web/key1?cas=97
false
In this case, the first CAS update succeeds because the ModifyIndex is 97.
However the second operation fails because the ModifyIndex is no longer 97.
We can also make use of the ModifyIndex to wait for a key's value to change.
For example, suppose we wanted to wait for key2 to be modified:
$ curl "http://localhost:8500/v1/kv/web/key2?index=101&wait=5s"
[{"CreateIndex":98,"ModifyIndex":101,"Key":"web/key2","Flags":42,"Value":"dGVzdA=="}]
By providing "?index=", we are asking to wait until the key has a ModifyIndex greater
than 101. However the "?wait=5s" parameter restricts the query to at most 5 seconds,
returning the current, unchanged value. This can be used to efficiently wait for
key modifications. Additionally, this same technique can be used to wait for a list
of keys, waiting only until any of the keys has a newer modification time.
Next Steps
These are only a few examples of what the API supports. For full documentation, please see the /kv/ route of the HTTP API.
Next, we will look at the web UI options supported by Consul.