# Redis

<https://redis.io/>

## Install

::::{tab-set}
:::{tab-item} Ubuntu
:sync: ubuntu

Add the repository:

```console
$ curl -fsSL https://packages.redis.io/gpg | sudo gpg --dearmor -o /usr/share/keyrings/redis-archive-keyring.gpg
$ echo "deb [signed-by=/usr/share/keyrings/redis-archive-keyring.gpg] https://packages.redis.io/deb $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/redis.list
deb [signed-by=/usr/share/keyrings/redis-archive-keyring.gpg] https://packages.redis.io/deb jammy main
```

Install:

```console
$ sudo apt update
$ sudo apt install redis
```

:::
::::

Check the version:

```console
$ redis-cli -v
redis-cli 8.0.1
```

## Configure

Edit file `/etc/redis/redis.conf` to enable cluster mode:

:::{literalinclude} /_files/ubuntu/etc/redis/redis.conf
:diff: /_files/ubuntu/etc/redis/redis.conf.orig
:::

:::{caution}
The protected mode is off and the service is opened to outside world, which is dangerous. The configurations is for learning and testing in internal network only.
:::

Start all nodes, then create the cluster:

```console
$ redis-cli --cluster create las0:6379 las1:6379 las2:6379
>>> Performing hash slots allocation on 3 nodes...
Master[0] -> Slots 0 - 5460
Master[1] -> Slots 5461 - 10922
Master[2] -> Slots 10923 - 16383
M: b099b5bbc985bd735380104d85b56577c7bb5e54 las0:6379
   slots:[0-5460] (5461 slots) master
M: 9b0c93352947c54494582c66e9afb1491f612325 las1:6379
   slots:[5461-10922] (5462 slots) master
M: 9baccecd0d7e6ae2730ef18f2f885843cfb2058d las2:6379
   slots:[10923-16383] (5461 slots) master
Can I set the above configuration? (type 'yes' to accept): yes
>>> Nodes configuration updated
>>> Assign a different config epoch to each node
>>> Sending CLUSTER MEET messages to join the cluster
Waiting for the cluster to join

>>> Performing Cluster Check (using node las0:6379)
M: b099b5bbc985bd735380104d85b56577c7bb5e54 las0:6379
   slots:[0-5460] (5461 slots) master
M: 9baccecd0d7e6ae2730ef18f2f885843cfb2058d 10.225.4.53:6379
   slots:[10923-16383] (5461 slots) master
M: 9b0c93352947c54494582c66e9afb1491f612325 10.225.4.52:6379
   slots:[5461-10922] (5462 slots) master
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
```

## Usage

In a Redis cluster, the key is hashed and distributed to so-called "slots" on each master node. To find the slot of a key:

```console
$ redis-cli cluster keyslot myKey
(integer) 16281
```

Set/Get data by key:

```console
$ redis-cli -c set myKey myValue
OK
$ redis-cli -c get myKey
"myValue"
```

If we do this in `redis-cli` prompts:

```console
$ redis-cli -c
127.0.0.1:6379> set myKey myNewValue
-> Redirected to slot [16281] located at 10.225.4.53:6379
OK
10.225.4.53:6379> get myKey
"myNewValue"
10.225.4.53:6379> exit
```

We can see additional messages of "Redirect". Note the `-c` parameter to invoke `redis-cli`, which is required to handle redirecting in cluster mode.