Maximum Pods per Cluster / Expected Pods per Node = Total Number of Nodes
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Planning
Initial Planning
For production environments, several factors influence installation. Consider the following questions as you read through the documentation:
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Which installation method do you want to use? The Installation Methods section provides some information about the quick and advanced installation methods.
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How many hosts do you require in the cluster? The Environment Scenarios section provides multiple examples of Single Master and Multiple Master configurations.
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How many pods are required in your cluster? The Sizing Considerations section provides limits for nodes and pods so you can calculate how large your environment needs to be.
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Is high availability required? High availability is recommended for fault tolerance. In this situation, you might aim to use the Multiple Masters Using Native HA example as a basis for your environment.
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Which installation type do you want to use: RPM or containerized? Both installations provide a working OpenShift Container Platform environment, but you might have a preference for a particular method of installing, managing, and updating your services.
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Is my installation supported if integrating with other technologies? See the OpenShift Container Platform Tested Integrations for a list of tested integrations.
Installation Methods
Both the quick and advanced installation methods are supported for development and production environments. If you want to quickly get OpenShift Container Platform up and running to try out for the first time, use the quick installer and let the interactive CLI guide you through the configuration options relevant to your environment.
For the most control over your cluster’s configuration, you can use the advanced installation method. This method is particularly suited if you are already familiar with Ansible. However, following along with the OpenShift Container Platform documentation should equip you with enough information to reliably deploy your cluster and continue to manage its configuration post-deployment using the provided Ansible playbooks directly.
If you install initially using the quick installer, you can always further tweak your cluster’s configuration and adjust the number of hosts in the cluster using the same installer tool. If you wanted to later switch to using the advanced method, you can create an inventory file for your configuration and carry on that way.
Sizing Considerations
Determine how many nodes and pods you require for your OpenShift Container Platform cluster. Cluster scalability correlates to the number of pods in a cluster environment. That number influences the other numbers in your setup.
The following table provides the maximum sizing limits for nodes and pods:
| Type | Maximum |
|---|---|
Maximum nodes per cluster |
1000 |
Maximum pods per cluster |
120,000 |
Maximum pods per node |
250 |
Maximum pods per core |
10 |
|
Oversubscribing the physical resources on a node affects resource guarantees the Kubernetes scheduler makes during pod placement. Learn what measures you can take to avoid memory swapping. |
Determine how many pods are expected to fit per node:
Example Scenario
If you want to scope your cluster for 2200 pods per cluster, you would need at least 9 nodes, assuming that there are 250 maximum pods per node:
2200 / 250 = 8.8
If you increase the number of nodes to 20, then the pod distribution changes to 110 pods per node:
2200 / 20 = 110
Environment Scenarios
This section outlines different examples of scenarios for your OpenShift Container Platform environment. Use these scenarios as a basis for planning your own OpenShift Container Platform cluster.
|
Moving from a single master cluster to multiple masters after installation is not supported. |
Single Master and Multiple Nodes
The following table describes an example environment for a single master (with embedded etcd) and two nodes:
| Host Name | Infrastructure Component to Install |
|---|---|
master.example.com |
Master and node |
node1.example.com |
Node |
node2.example.com |
Single Master, Multiple etcd, and Multiple Nodes
The following table describes an example environment for a single master, three etcd hosts, and two nodes:
| Host Name | Infrastructure Component to Install |
|---|---|
master.example.com |
Master and node |
etcd1.example.com |
etcd |
etcd2.example.com |
|
etcd3.example.com |
|
node1.example.com |
Node |
node2.example.com |
|
When specifying multiple etcd hosts, external etcd is installed and configured. Clustering of OpenShift Container Platform’s embedded etcd is not supported. |
Multiple Masters Using Native HA
The following describes an example environment for three
masters,
one HAProxy load balancer, three
etcd
hosts, and two
nodes
using the native HA method:
| Host Name | Infrastructure Component to Install |
|---|---|
master1.example.com |
Master (clustered using native HA) and node |
master2.example.com |
|
master3.example.com |
|
lb.example.com |
HAProxy to load balance API master endpoints |
etcd1.example.com |
etcd |
etcd2.example.com |
|
etcd3.example.com |
|
node1.example.com |
Node |
node2.example.com |
|
When specifying multiple etcd hosts, external etcd is installed and configured. Clustering of OpenShift Container Platform’s embedded etcd is not supported. |
Stand-alone Registry
You can also install OpenShift Container Platform to act as a stand-alone registry using the OpenShift Container Platform’s integrated registry. See Installing a Stand-alone Registry for details on this scenario.
RPM vs Containerized
An RPM installation installs all services through package management and configures services to run within the same user space, while a containerized installation configures installs services using container images and runs separate services in individual containers.
The default method for installing OpenShift Container Platform on Red Hat Enterprise Linux (RHEL) uses RPMs. Alternatively, you can use the containerized method, which deploys containerized OpenShift Container Platform master and node components. When targeting a RHEL Atomic Host system, the containerized method is the only available option, and is automatically selected for you based on the detection of the /run/ostree-booted file.
The following table outlines the differences between the RPM and Containerized methods:
| Type | RPM | Containerized |
|---|---|---|
Installation Method |
Packages via |
Container images via |
Service Management |
|
|
Operating System |
Red Hat Enterprise Linux |
Red Hat Enterprise Linux or Red Hat Atomic Host |
The Containerized Installation Preparation section provides more details on configuring your installation to use containerized services.