How to scale horizontally

Horizontal scaling of a Valkey deployment is done by adding and removing Juju units.

Add a unit

To add additional units to your deployed Valkey application, run the following command:

juju add-unit valkey -n 1

Where -n 1 specifies the number of units to add.

You can now watch the new unit join the deployment with watch juju status. It usually takes a few minutes for a unit to be added to an existing deployment.

Model     Controller      Cloud/Region        Version  SLA          Timestamp
tutorial  k8s-controller  microk8s/localhost  3.6.14   unsupported  19:21:12+01:00

App                       Version  Status  Scale  Charm                     Channel   Rev  Address         Exposed  Message
self-signed-certificates           active      1  self-signed-certificates  1/stable  586  10.152.183.111  no       
valkey                             active      4  valkey                    9/edge     11  10.152.183.123  no       

Unit                         Workload  Agent  Address      Ports  Message
self-signed-certificates/0*  active    idle   10.1.44.89          
valkey/0*                    active    idle   10.1.44.126         
valkey/1                     active    idle   10.1.44.117         
valkey/2                     active    idle   10.1.44.127         
valkey/3                     active    idle   10.1.44.68

Remove units

Removing a unit from the application scales down the application. If you currently have four units, then only one is the primary and three are replicas. Removing a unit will reduce the number of replicas to two and the total number of units to three.

Before scaling down, list all the units with juju status:

  • valkey/0

  • valkey/1

  • valkey/2

  • valkey/3

To scale the application down to three units, run:

juju remove-unit valkey --num-units 1

Safely removing the unit will take a few moments. You’ll know that the unit was successfully removed when juju status reports all units active/idle again:

Model     Controller      Cloud/Region        Version  SLA          Timestamp
tutorial  k8s-controller  microk8s/localhost  3.6.14   unsupported  19:23:44+01:00

App                       Version  Status  Scale  Charm                     Channel   Rev  Address         Exposed  Message
self-signed-certificates           active      1  self-signed-certificates  1/stable  586  10.152.183.111  no       
valkey                             active      3  valkey                    9/edge     11  10.152.183.123  no       

Unit                         Workload  Agent  Address      Ports  Message
self-signed-certificates/0*  active    idle   10.1.44.89          
valkey/0*                    active    idle   10.1.44.126         
valkey/1                     active    idle   10.1.44.117         
valkey/2                     active    idle   10.1.44.127