In addition to providing service discovery, integrated health checking, and securing network traffic, Consul includes a key value store, which you can use to dynamically configure applications, coordinate services, manage leader election, or serve as a data backend for Vault, along with a myriad of other uses.
In this tutorial, you will explore the Consul key value store (Consul KV) using the
command line. The tutorial assumes that the Consul agent from the Run the Consul Agent tutorial is
still running. If not you can start a new one by running consul agent -dev.
Consul KV is enabled automatically on Consul agents; you don't need to enable it
in Consul's configuration.
There are two ways to interact with the Consul KV store: the Consul CLI and UI. In this tutorial, you will use the CLI.
»Add data
First, insert or "put" some values into the KV store with the consul kv put
command. The first entry after the command is the key, and the second entry is
the value.
$ consul kv put redis/config/minconns 1
Success! Data written to: redis/config/minconns
Here the key is redis/config/maxconns and the value is set to 25.
$ consul kv put redis/config/maxconns 25
Success! Data written to: redis/config/maxconns
Notice that with the key entered below ("redis/config/users/admin"), you set
a flags value of 42. Keys support setting a 64-bit integer flag value that
isn't used internally by Consul, but can be used by clients to add metadata to
any KV pair.
$ consul kv put -flags=42 redis/config/users/admin abcd1234
Success! Data written to: redis/config/users/admin
»Query data
Now, query for the value of one of the keys you just entered.
$ consul kv get redis/config/minconns
1
Consul retains some additional metadata about the key-value pair. Retrieve the
some metadata (including the "flag" you set) using the -detailed command line
flag.
$ consul kv get -detailed redis/config/users/admin
CreateIndex 14
Flags 42
Key redis/config/users/admin
LockIndex 0
ModifyIndex 14
Session -
Value abcd1234
List all the keys in the store using the recurse options. Results are returned
in lexicographical order.
$ consul kv get -recurse
redis/config/maxconns:25
redis/config/minconns:1
redis/config/users/admin:abcd1234
»Delete data
Delete a key from the Consul KV store, issue a "delete" call.
$ consul kv delete redis/config/minconns
Success! Deleted key: redis/config/minconns
Consul lets you interact with keys in a folder-like way. Although all the keys in the KV store are actually stored flat, Consul allows you to manipulate keys that share a certain prefix as a group, as if they were in folders or subfolders.
Delete all the keys with the redis prefix using the recurse option.
$ consul kv delete -recurse redis
Success! Deleted keys with prefix: redis
»Modify existing data
Update the value of an existing key.
$ consul kv put foo bar
Success! Data written to: foo
Get the updated key.
$ consul kv get foo
bar
Put the new value at an extant "path".
$ consul kv put foo zip
Success! Data written to: foo
Check the updated path.
$ consul kv get foo
zip
»Next steps
In this tutorial, you added, viewed, modified, and deleted entries in Consul's key value store.
Consul can perform atomic key updates using a Check-And-Set (CAS) operation, and
includes other sophisticated options for writing keys and values. You can
explore these options on the help page for the consul kv put command.
$ consul kv put -h
These are only a few examples of what the API supports. For the complete documentation, please see the HTTP API documentation and CLI documentation.
Now that Consul contains some interesting data including service registrations, keys, values, and intentions, continue to the Explore the Consul UI tutorial to locate all this data in the Consul web UI.