[Tutorial] Redis Cluster Using Juju


#1

Redis-Cluster

My redis-cluster is ever growing, as such I thought it would be wise to get a working piece of automation around it.

30 Second Overview

The redis charm has gained a new functionality that allows it to be deployed in cluster mode. To run Redis in cluster mode, just set cluster-enabled to true when you deploy the charm. This will tell Redis to configure itself in cluster mode. Some lifecycle automation has been added to the charm to facilitate auto-rebalancing when units are added or removed.

Component Github Charmstore
redis layer-redis cs:~omnivector/redis
interface-redis
juju deploy cs:~omnivector/redis -n9 --config cluster-enabled=true

Gives us

Model              Controller  Cloud/Region   Version  SLA          Timestamp
bdx-redis-test-00  pdl-aws     aws/us-west-2  2.5.4    unsupported  15:54:16Z

App    Version  Status  Scale  Charm  Store       Rev  OS      Notes
redis  5.0.3    active      9  redis  jujucharms   17  ubuntu

Unit      Workload  Agent      Machine  Public address  Ports     Message
redis/15  active    idle       15       172.31.102.4    6379/tcp  successfully clustered
redis/16  active    idle       16       172.31.102.41   6379/tcp  successfully clustered
redis/17  active    idle       17       172.31.102.121  6379/tcp  successfully clustered
redis/18  active    idle       18       172.31.102.8    6379/tcp  successfully clustered
redis/19  active    idle       19       172.31.103.174  6379/tcp  successfully clustered
redis/20  active    idle       20       172.31.104.59   6379/tcp  successfully clustered
redis/21  active    idle       21       172.31.104.231  6379/tcp  successfully clustered
redis/22  active    idle       22       172.31.103.120  6379/tcp  successfully clustered
redis/23  active    idle       23       172.31.103.145  6379/tcp  successfully clustered

Machine  State    DNS             Inst id              Series  AZ          Message
15       started  172.31.102.4    i-02b2a4c978a601800  bionic  us-west-2a  running
16       started  172.31.102.41   i-063d5b602cde3155c  bionic  us-west-2a  running
17       started  172.31.102.121  i-056926746e9fe85ef  bionic  us-west-2a  running
18       started  172.31.102.8    i-003d79f51b8db8cf2  bionic  us-west-2a  running
19       started  172.31.103.174  i-02225abf5b11e1a95  bionic  us-west-2b  running
20       started  172.31.104.59   i-0ea30e9c40a53b9bd  bionic  us-west-2c  running
21       started  172.31.104.231  i-064a3a6f185a1915a  bionic  us-west-2c  running
22       started  172.31.103.120  i-03a0e74ab9d23be87  bionic  us-west-2b  running
23       started  172.31.103.145  i-02f12d738ec0f9f04  bionic  us-west-2b  running

We can use the redis-cli to verify the node/slot configuration is as intended (balanced).

juju run --unit redis/15 "/snap/bin/redis-bdx.redis-cli cluster nodes"
ff3f173df80e284af39be70d94fc55ec946031ed 172.31.103.174:6379@16379 master - 0 1556985285031 7 connected 680-819 1365-1484 2731-3120 5462-5851 8193-8582 13654-14043
0b32363760c35c5545ec32c454b0067ce7fc461f 172.31.104.59:6379@16379 master - 0 1556985285834 8 connected 228-295 394-549 820-955 1485-1776 3121-3412 5852-6143 8583-8874 14044-14335
e80fc21cd4191dddfea414083d350ed2ec7c6c21 172.31.104.231:6379@16379 master - 0 1556985285000 4 connected 6372-6826 10923-12287
8d4d4bd45943a9dea0b4e750fc3717575639c5d3 172.31.102.41:6379@16379 master - 0 1556985284000 5 connected 2005-2184 6827-7646 12288-13107
9bdd424266aa237cd539851344da28962bdb45ba 172.31.102.121:6379@16379 master - 0 1556985284829 6 connected 1184-1364 2185-2730 5461 7647-8192 13108-13653
0a932ed5563ac81693156e6d0bf5161ab5a1b941 172.31.102.4:6379@16379 myself,master - 0 1556985283000 3 connected 14564-16383
00fe7e2a9448d9810641bb277c0f57a33c2e150b 172.31.103.120:6379@16379 master - 0 1556985285000 9 connected 0-227 296-393 550-679 956-1183 1777-2004 3413-3640 6144-6371 8875-9102 14336-14563
75b84942a6d8d31bd30d89ec96e23e028fbb1189 172.31.102.8:6379@16379 master - 0 1556985284528 1 connected 3641-5460
534b6b989f3bec8cb841c9ef2a03d52573976a82 172.31.103.145:6379@16379 master - 0 1556985284000 2 connected 9103-10922

Example Rebalancing

This charm will automatically rebalance slots to other nodes in the cluster when a unit is pragmatically added or removed.

Scale Down

Let’s remove a few units and see what happens.

$ juju remove-unit redis/21
removing unit redis/21

$ juju remove-unit redis/22
removing unit redis/22

$ juju remove-unit redis/23
removing unit redis/23

Now run redis-bdx.redis-cli cluster nodes to see that only 6 nodes exist and contain all of the slots that were previously on the nodes we removed.

 juju run --unit redis/3 "/snap/bin/redis-bdx.redis-cli cluster nodes"
139e305fab256c675909a1cd5504194ef79b55ed 172.31.104.137:6379@16379 master - 0 1556984153564 27 connected 2005-2184 3804-4193 6827-7646 8059-8192 12288-13201 14629-14921
883eebfe36c773c5a48b40cc4bd2d86879431517 172.31.102.83:6379@16379 master - 0 1556984153063 26 connected 1184-1364 2185-2231 2688-2730 3641-3803 5461 7647-7830 9103-10922 15508-15799
35f0715fb296aaa75efd1486e981738b5fd6437f 172.31.104.4:6379@16379 myself,master - 0 1556984152000 31 connected 228-549 820-955 5364-5460 5462-6143 7831-8058 8193-8872 13202-13429 14564-14628 16092-16383
ea8ec8f18d808648802e407c2c5438d6144289b7 172.31.103.243:6379@16379 master - 0 1556984153564 30 connected 2460-2687 4974-5363 6372-6826 10923-12287 15800-16091
0663529d652411e0292b34d36b521ad90f8d0eef 172.31.102.238:6379@16379 master - 0 1556984152562 28 connected 778-819 1365-1776 2232-2459 2731-3412 4194-4583 8873-8874 13654-14335 14922-15214
d81963c014b2b860640d79fb9fb884a383f5edb1 172.31.103.194:6379@16379 master - 0 1556984154565 29 connected 0-227 550-777 956-1183 1777-2004 3413-3640 4584-4973 6144-6371 8875-9102 13430-13653 14336-14563 15215-15507

As you can see the slots from units 1, 2, and 3 have been rebalanced to the remaining nodes.

Scale Up

Add another few units to our cluster of now 6 nodes (as we removed 3 in the last step).

juju add-unit redis -n 6

After the nodes have settled, go ahead and check your slots/nodes again to see the new node additions have been added to the cluster and the slots rebalanced to the new nodes appropriately.


Juju 2.6.1 Release Notes
WIP - Juju 2.6.1 Release Notes
#2

This is killer, James.

The promulgated Redis charm is quite venerable, and does not expose clustering support.

Redis is so good that I am surprised not to see it in more Juju software stacks.