Chapter 3. Scaling RHMAP Core application
This guide explains how to horizontally scale RHMAP Core components. OpenShift pod scaling allows to react to changes in traffic and allocate the necessary resources to handle current demand. Pods can be scaled manually or automatically, based on resource usage. For more information please refer to OpenShift documentation.
3.1. Scaling pods
RHMAP Core pods can be scaled using either oc command tool or web console.
To scale pods execute following commands:
Target oc tool to RHMAP OpenShift master
oc login http://yourcluster.url
Fetch all RHMAP Core deployment configurations to get name of component you want to scale
oc get dc
To scale any of deployment configurations execute:
oc scale --replicas=2 dc name
Where
namerepresents deployment configuration name returned by previous command.
OpenShift3 also supports autoscaling that would allow components to scale based on resource usage. For more information please refer to OpenShift documentation.
3.2. Example replica configuration for Core
Example commands that would scale most used components:
oc scale --replicas=2 dc fh-ngui oc scale --replicas=2 dc millicore oc scale --replicas=2 dc fh-supercore oc scale --replicas=2 dc fh-aaa oc scale --replicas=2 dc ups
3.3. Limitations
Not all RHMAP Core pods can be scaled using OpenShift api.
3.3.1. Database and cache pods
Increasing the replica count to more than one for any of these pods is not supported. Scaling following pods to more than one replica may cause loss of data and make platform unstable.
| Component | Reason |
|---|---|
| mysql | Mysql is currently a standalone instance without support for master slave replication. |
| mongodb | Mongdb is a standalone instance that is not part of a replica set. |
| memcached | Not configured for replication. Core components are configured use single memcached instance. |
| redis | Not configured for replication. Core components are configured use single redis instance. |
3.3.2. Storage and monitoring components
| Component | Reason |
|---|---|
| gitlab-shell | Git repository data cannot be shared between nodes |
| fh-scm | Git repository data cannot be shared between nodes |
| nagios | Monitoring service - only one instance needed. Multiple instances of this pod may cause alert duplication. |
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