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System and environment requirements | Installing Clusters | OKD 3.11
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System and environment requirements

System requirements

The hosts in your OKD environment must meet the following hardware specifications and system-level requirements.

Minimum hardware requirements

The system requirements vary per host type:

masters

  • Physical or virtual system or an instance running on a public or private IaaS.

  • Base OS: Fedora 21, CentOS 7.5, Red Hat Enterprise Linux (RHEL) 7.5 or later with the "Minimal" installation option and the latest packages from the Extras channel, or RHEL Atomic Host 7.4.5 or later. If you use RHEL, you must use the following minimal kernel versions:

    • RHEL 7.5: 3.10.0-862.31.1

    • RHEL 7.6: 3.10.0-957.27.2

    • RHEL 7.7: 3.10.0-1062

  • Minimum 4 vCPU (additional are strongly recommended).

  • Minimum 16 GB RAM (additional memory is strongly recommended, especially if etcd is co-located on masters).

  • Minimum 40 GB hard disk space for the file system containing /var/. redcircle 1

  • Minimum 1 GB hard disk space for the file system containing /usr/local/bin/.

  • Minimum 1 GB hard disk space for the file system containing the system’s temporary directory. redcircle 2

  • masters with a co-located etcd require a minimum of 4 cores. Two-core systems do not work.

Nodes

  • Physical or virtual system, or an instance running on a public or private IaaS.

  • Base OS: Fedora 21, CentOS 7.5, RHEL 7.5 or later with "Minimal" installation option, or RHEL Atomic Host 7.4.5 or later. If you use RHEL, you must use the following minimal kernel versions:

    • RHEL 7.5: 3.10.0-862.31.1

    • RHEL 7.6: 3.10.0-957.27.2

    • RHEL 7.7: 3.10.0-1062

  • NetworkManager 1.0 or later.

  • 1 vCPU.

  • Minimum 8 GB RAM.

  • Minimum 15 GB hard disk space for the file system containing /var/. redcircle 1

  • Minimum 1 GB hard disk space for the file system containing /usr/local/bin/.

  • Minimum 1 GB hard disk space for the file system containing the system’s temporary directory. redcircle 2

  • An additional minimum 15 GB unallocated space per system running containers for Docker’s storage back end; see Configuring Docker Storage. Additional space might be required, depending on the size and number of containers that run on the node.

External etcd Nodes

Ansible controller

The host that you run the Ansible playbook on must have at least 75MiB of free memory per host in the inventory.

redcircle 1 Meeting the /var/ file system sizing requirements in RHEL Atomic Host requires making changes to the default configuration. See Managing Storage with Docker-formatted Containers for instructions on configuring this during or after installation.

redcircle 2 The system’s temporary directory is determined according to the rules defined in the tempfile module in Python’s standard library.

You must configure storage for each system that runs a container daemon. For containerized installations, you need storage on masters. Also, by default, the web console runs in containers on masters, and masters need storage to run the web console. Containers run on nodes, so nodes always require storage. The size of storage depends on workload, the number of containers, the size of the running containers, and the containers' storage requirements. You must also configure storage to run containerized etcd.

It is highly recommended that you use etcd with storage that handles serial writes (fsync) quickly, such as NVMe or SSD. Ceph, NFS, and spinning disks are not recommended.

Production level hardware requirements

Test or sample environments function with the minimum requirements. For production environments, the following recommendations apply:

master hosts

In a highly available OKD cluster with external etcd, a master host needs to meet the minimum requirements and have 1 CPU core and 1.5 GB of memory for each 1000 pods. Therefore, the recommended size of a master host in an OKD cluster of 2000 pods is the minimum requirements of 2 CPU cores and 16 GB of RAM, plus 2 CPU cores and 3 GB of RAM, totaling 4 CPU cores and 19 GB of RAM.

See Recommended Practices for OKD master Hosts for performance guidance.

Node hosts

The size of a node host depends on the expected size of its workload. As an OKD cluster administrator, you need to calculate the expected workload and add about 10 percent for overhead. For production environments, allocate enough resources so that a node host failure does not affect your maximum capacity.

For more information, see Sizing Considerations and Cluster Limits.

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.

Storage management

Table 1. The main directories to which OKD components write data
Directory Notes Sizing Expected Growth

/var/lib/openshift

Used for etcd storage only when in single master mode and etcd is embedded in the atomic-openshift-master process.

Less than 10GB.

Will grow slowly with the environment. Only storing metadata.

/var/lib/etcd

Used for etcd storage when in Multi-master mode or when etcd is made standalone by an administrator.

Less than 20 GB.

Will grow slowly with the environment. Only storing metadata.

/var/lib/docker

When the run time is docker, this is the mount point. Storage used for active container runtimes (including pods) and storage of local images (not used for registry storage). Mount point should be managed by docker-storage rather than manually.

50 GB for a Node with 16 GB memory.

Additional 20-25 GB for every additional 8 GB of memory.

Growth is limited by the capacity for running containers.

/var/lib/containers

When the run time is CRI-O, this is the mount point. Storage used for active container runtimes (including pods) and storage of local images (not used for registry storage).

50 GB for a Node with 16 GB memory.

Additional 20-25 GB for every additional 8 GB of memory.

Growth limited by capacity for running containers

/var/lib/origin/openshift.local.volumes

Ephemeral volume storage for pods. This includes anything external that is mounted into a container at runtime. Includes environment variables, kube secrets, and data volumes not backed by persistent storage PVs.

Varies

Minimal if pods requiring storage are using persistent volumes. If using ephemeral storage, this can grow quickly.

/var/log

Log files for all components.

10 to 30 GB.

Log files can grow quickly; size can be managed by growing disks or managed using log rotate.

GlusterFS hardware requirements

Any nodes used in a Containerized GlusterFS or External GlusterFS cluster are considered storage nodes. Storage nodes can be grouped into distinct cluster groups, though a single node can not be in multiple groups. For each group of storage nodes:

  • A minimum of one or more storage nodes per group is required based on storage gluster volumetype option.

  • Each storage node must have a minimum of 8 GB of RAM. This is to allow running the GlusterFS pods, as well as other applications and the underlying operating system.

    • Each GlusterFS volume also consumes memory on every storage node in its storage cluster, which is about 30 MB. The total amount of RAM should be determined based on how many concurrent volumes are desired or anticipated.

  • Each storage node must have at least one raw block device with no present data or metadata. These block devices will be used in their entirety for GlusterFS storage. Make sure the following are not present:

    • Partition tables (GPT or MSDOS)

    • Filesystems or residual filesystem signatures

    • LVM2 signatures of former Volume Groups and Logical Volumes

    • LVM2 metadata of LVM2 physical volumes

    If in doubt, wipefs -a <device> should clear any of the above.

It is recommended to plan for two clusters: one dedicated to storage for infrastructure applications (such as an OpenShift Container Registry) and one dedicated to storage for general applications. This would require a total of six storage nodes. This recommendation is made to avoid potential impacts on performance in I/O and volume creation.

Monitoring hardware requirements

The monitoring stack imposes additional system resource requirements and is installed by default. See the computing resources recommendations and the cluster monitoring documentation.

SELinux requirements

Security-Enhanced Linux (SELinux) must be enabled on all of the servers before installing OKD or the installer will fail. Also, configure SELINUX=enforcing and SELINUXTYPE=targeted in the /etc/selinux/config file:

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
SELINUX=enforcing
# SELINUXTYPE= can take one of these three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected.
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted

Optional: Configuring Core Usage

By default, OKD masters and nodes use all available cores in the system they run on. You can choose the number of cores you want OKD to use by setting the GOMAXPROCS environment variable. See the Go Language documentation for more information, including how the GOMAXPROCS environment variable works.

For example, run the following before starting the server to make OKD only run on one core:

# export GOMAXPROCS=1

Alternatively, if you plan to getting_started/administrators.adoc#running-in-a-docker-container[run OpenShift in a container], add -e GOMAXPROCS=1 to the docker run command when launching the server.

Optional: Using OverlayFS

OverlayFS is a union file system that allows you to overlay one file system on top of another.

As of Red Hat Enterprise Linux 7.4, you have the option to configure your OKD environment to use OverlayFS. The overlay2 graph driver is fully supported in addition to the older overlay driver. However, Red Hat recommends using overlay2 instead of overlay, because of its speed and simple implementation.

Comparing the Overlay Versus Overlay2 Graph Drivers has more information about the overlay and overlay2 drivers.

See the Overlay Graph Driver section of the Atomic Host documentation for instructions on how to enable the overlay2 graph driver for the Docker service.

Security Warning

OKD runs containers on hosts in the cluster, and in some cases, such as build operations and the registry service, it does so using privileged containers. Furthermore, those containers access the hosts' Docker daemon and perform docker build and docker push operations. As such, cluster administrators must be aware of the inherent security risks associated with performing docker run operations on arbitrary images as they effectively have root access. This is particularly relevant for docker build operations.

Exposure to harmful containers can be limited by assigning specific builds to nodes so that any exposure is limited to those nodes. To do this, see the Assigning Builds to Specific Nodes section of the Developer Guide. For cluster administrators, see the Configuring Global Build Defaults and Overrides topic.

You can also use security context constraints to control the actions that a pod can perform and what it has the ability to access. For instructions on how to enable images to run with USER in the Dockerfile, see Managing Security Context Constraints (requires a user with cluster-admin privileges).

For more information, see these articles:

Environment Requirements

The following section defines the requirements of the environment containing your OKD configuration. This includes networking considerations and access to external services, such as Git repository access, storage, and cloud infrastructure providers.

DNS Requirements

OKD requires a fully functional DNS server in the environment. This is ideally a separate host running DNS software and can provide name resolution to hosts and containers running on the platform.

Adding entries into the /etc/hosts file on each host is not enough. This file is not copied into containers running on the platform.

Key components of OKD run themselves inside of containers and use the following process for name resolution:

  1. By default, containers receive their DNS configuration file (/etc/resolv.conf) from their host.

  2. OKD then sets the pod’s first nameserver to the IP address of the node.

As of OKD 1.2, dnsmasq is automatically configured on all masters and nodes. The pods use the nodes as their DNS, and the nodes forward the requests. By default, dnsmasq is configured on the nodes to listen on port 53, therefore the nodes cannot run any other type of DNS application.

NetworkManager, a program for providing detection and configuration for systems to automatically connect to the network, is required on the nodes in order to populate dnsmasq with the DNS IP addresses.

NM_CONTROLLED is set to yes by default. If NM_CONTROLLED is set to no, then the NetworkManager dispatch script does not create the relevant origin-upstream-dns.conf dnsmasq file, and you must configure dnsmasq manually.

Similarly, if the PEERDNS parameter is set to no in the network script, for example, /etc/sysconfig/network-scripts/ifcfg-em1, then the dnsmasq files are not generated, and the Ansible install will fail. Ensure the PEERDNS setting is set to yes.

The following is an example set of DNS records:

master1    A   10.64.33.100
master2    A   10.64.33.103
node1      A   10.64.33.101
node2      A   10.64.33.102

If you do not have a properly functioning DNS environment, you might experience failure with:

  • Product installation via the reference Ansible-based scripts

  • Deployment of the infrastructure containers (registry, routers)

  • Access to the OKD web console, because it is not accessible via IP address alone

Configuring Hosts to Use DNS

Make sure each host in your environment is configured to resolve hostnames from your DNS server. The configuration for hosts' DNS resolution depend on whether DHCP is enabled. If DHCP is:

  • Disabled, then configure your network interface to be static, and add DNS nameservers to NetworkManager.

  • Enabled, then the NetworkManager dispatch script automatically configures DNS based on the DHCP configuration.

To verify that hosts can be resolved by your DNS server:

  1. Check the contents of /etc/resolv.conf:

    $ cat /etc/resolv.conf
# Generated by NetworkManager
search example.com
nameserver 10.64.33.1
# nameserver updated by /etc/NetworkManager/dispatcher.d/99-origin-dns.sh

    In this example, 10.64.33.1 is the address of our DNS server.

  2. Test that the DNS servers listed in /etc/resolv.conf are able to resolve host names to the IP addresses of all masters and nodes in your OKD environment:

    $ dig <node_hostname> @<IP_address> +short

    For example:

    $ dig master.example.com @10.64.33.1 +short
10.64.33.100
$ dig node1.example.com @10.64.33.1 +short
10.64.33.101

Configuring a DNS Wildcard

Optionally, configure a wildcard for the router to use, so that you do not need to update your DNS configuration when new routes are added. If you configure a wildcard for the router, set the openshift_master_default_subdomain parameter to this value when you configure the Ansible inventory file.

A wildcard for a DNS zone must ultimately resolve to the IP address of the OKD router.

For example, create a wildcard DNS entry for cloudapps that has a low time-to-live value (TTL) and points to the public IP address of the host where the router will be deployed:

*.cloudapps.example.com. 300 IN  A 192.168.133.2

In your /etc/resolv.conf file on each node host, ensure that the DNS server that has the wildcard entry is not listed as a nameserver or that the wildcard domain is not listed in the search list. Otherwise, containers managed by OKD might fail to resolve host names properly.

Configuring Node Host Names

When you set up a cluster that is not integrated with a cloud provider, you must correctly set your nodes' host names. Each node’s host name must be resolvable, and each node must be able to reach each other node.

To confirm that a node can reach another node:

  1. On one node, obtain the host name:

    $ hostname

master-1.example.com

  2. On that same node, obtain the fully qualified domain name of the host:

    $ hostname -f

master-1.example.com

  3. From a different node, confirm that you can reach the first node:

    $ ping master-1.example.com -c 1

PING master-1.example.com (172.16.122.9) 56(84) bytes of data.
64 bytes from master-1.example.com (172.16.122.9): icmp_seq=1 ttl=64 time=0.319 ms

--- master-1.example.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.319/0.319/0.319/0.000 ms

Network Access Requirements

A shared network must exist between the master and node hosts. If you plan to configure multiple masters for high-availability using standard cluster installation process, you must also select an IP to be configured as your virtual IP (VIP) during the installation process. The IP that you select must be routable between all of your nodes, and if you configure using a FQDN it must resolve on all nodes.

NetworkManager

NetworkManager, a program for providing detection and configuration for systems to automatically connect to the network, is required on the nodes in order to populate dnsmasq with the DNS IP addresses.

NM_CONTROLLED is set to yes by default. If NM_CONTROLLED is set to no, then the NetworkManager dispatch script does not create the relevant origin-upstream-dns.conf dnsmasq file, and you must configure dnsmasq manually.

Configuring firewalld as the firewall

While iptables is the default firewall, firewalld is recommended for new installations. You can enable firewalld by setting os_firewall_use_firewalld=true in the Ansible inventory file.

[OSEv3:vars]
os_firewall_use_firewalld=True

Setting this variable to true opens the required ports and adds rules to the default zone, which ensure that firewalld is configured correctly.

Using the firewalld default configuration comes with limited configuration options, and cannot be overridden. For example, while you can set up a storage network with interfaces in multiple zones, the interface that nodes communicate on must be in the default zone.

Hosts with Multiple Network Interfaces

If a host has more then one network interface, OKD uses only one network interface for installation, the cluster network, and the service network. You can use additional network interfaces for communication that is not related to OKD, but there is no support to route some cluster-related traffic over one network interface and different cluster-related traffic over another network interface.

Required Ports

The OKD installation automatically creates a set of internal firewall rules on each host using iptables. However, if your network configuration uses an external firewall, such as a hardware-based firewall, you must ensure infrastructure components can communicate with each other through specific ports that act as communication endpoints for certain processes or services.

Ensure the following ports required by OKD are open on your network and configured to allow access between hosts. Some ports are optional depending on your configuration and usage.

Table 2. Node to Node

4789

UDP

Required for SDN communication between pods on separate hosts.
Table 3. Nodes to master

4789

UDP

Required for SDN communication between pods on separate hosts.

443 or 8443

TCP

Required for node hosts to communicate to the master API, for the node hosts to post back status, to receive tasks, and so on.
Table 4. master to Node

4789

UDP

Required for SDN communication between pods on separate hosts.

10250

TCP

The master proxies to node hosts via the Kubelet for oc commands. This port must to be allowed from masters and infra nodes to any master and node. For metrics, the source must be the infra nodes.

10010

TCP

If using CRI-O, open this port to allow oc exec and oc rsh operations.
Table 5. master to master

2049

TCP/UDP

Required when provisioning an NFS host as part of the installer.

2379

TCP

Used for standalone etcd (clustered) to accept changes in state.

2380

TCP

etcd requires this port be open between masters for leader election and peering connections when using standalone etcd (clustered).

4789

UDP

Required for SDN communication between pods on separate hosts.
Table 6. External to Load Balancer

9000

TCP

If you choose the native HA method, optional to allow access to the HAProxy statistics page.
Table 7. External to master

443 or 8443

TCP

Required for node hosts to communicate to the master API, for node hosts to post back status, to receive tasks, and so on.

8444

TCP

Port that the controller manager and scheduler services listen on. Required to be open for the /metrics and /healthz endpoints.
Table 8. IaaS Deployments

22

TCP

Required for SSH by the installer or system administrator.

53 or 8053

TCP/UDP

Required for DNS resolution of cluster services (SkyDNS). Installations prior to 1.2 or environments upgraded to 1.2 use port 53. New installations will use 8053 by default so that dnsmasq might be configured. Only required to be internally open on master hosts.

80 or 443

TCP

For HTTP/HTTPS use for the router. Required to be externally open on node hosts, especially on nodes running the router.

1936

TCP

(Optional) Required to be open when running the template router to access statistics. Can be open externally or internally to connections depending on if you want the statistics to be expressed publicly. Can require extra configuration to open. See the Notes section below for more information.

2379 and 2380

TCP

For standalone etcd use. Only required to be internally open on the master host. 2379 is for server-client connections. 2380 is for server-server connections, and is only required if you have clustered etcd.

4789

UDP

For VxLAN use (OpenShift SDN). Required only internally on node hosts.

8443

TCP

For use by the OKD web console, shared with the API server.

10250

TCP

For use by the Kubelet. Required to be externally open on nodes.

Notes

  • In the above examples, port 4789 is used for User Datagram Protocol (UDP).

  • When deployments are using the SDN, the pod network is accessed via a service proxy, unless it is accessing the registry from the same node the registry is deployed on.

  • OKD internal DNS cannot be received over SDN. For non-cloud deployments, this will default to the IP address associated with the default route on the master host. For cloud deployments, it will default to the IP address associated with the first internal interface as defined by the cloud metadata.

  • The master host uses port 10250 to reach the nodes and does not go over SDN. It depends on the target host of the deployment and uses the computed value of openshift_public_hostname.

  • Port 1936 can still be inaccessible due to your iptables rules. Use the following to configure iptables to open port 1936:

    # iptables -A OS_FIREWALL_ALLOW -p tcp -m state --state NEW -m tcp \
    --dport 1936 -j ACCEPT
Table 9. Aggregated Logging and Metrics

9200

TCP

For Elasticsearch API use. Required to be internally open on any infrastructure nodes so Kibana is able to retrieve logs for display. It can be externally open for direct access to Elasticsearch by means of a route. The route can be created using oc expose.

9300

TCP

For Elasticsearch inter-cluster use. Required to be internally open on any infrastructure node so the members of the Elasticsearch cluster might communicate with each other.

9090

TCP

For Prometheus API and web console use.

9100

TCP

For the Prometheus Node-Exporter, which exports hardware and operating system metrics. Port 9100 needs to be open on each OKD host in order for the Prometheus server to scrape the metrics.

8443

TCP

For node hosts to communicate to the master API, for the node hosts to post back status, to receive tasks, and so on. This port needs to be allowed from masters and infra nodes to any master and node.

10250

TCP

For the Kubernetes cAdvisor, a container resource usage and performance analysis agent. This port must to be allowed from masters and infra nodes to any master and node. For metrics, the source must be the infra nodes.

8444

TCP

Port that the controller manager and scheduler services listen on. Port 8444 must be open on each OKD host.

1936

TCP

(Optional) Required to be open when running the template router to access statistics. This port must be allowed from the infra nodes to any infra nodes hosting the routers if Prometheus metrics are enabled on routers. Can be open externally or internally to connections depending on if you want the statistics to be expressed publicly. Can require extra configuration to open. See the Notes section above for more information.

Notes

Persistent Storage

The Kubernetes persistent volume framework allows you to provision an OKD cluster with persistent storage using networked storage available in your environment. This can be done after completing the initial OKD installation depending on your application needs, giving users a way to request those resources without having any knowledge of the underlying infrastructure.

The Configuring Clusters guide provides instructions for cluster administrators on provisioning an OKD cluster with persistent storage using NFS, GlusterFS, Ceph RBD, OpenStack Cinder, AWS Elastic Block Store (EBS), GCE Persistent Disks, and iSCSI.

Cloud Provider Considerations

There are certain aspects to take into consideration if installing OKD on a cloud provider.

Overriding Detected IP Addresses and Host Names

Some deployments require that the user override the detected host names and IP addresses for the hosts. To see the default values, change to the playbook directory and run the openshift_facts playbook:

$ cd /usr/share/ansible/openshift-ansible
$ ansible-playbook  [-i /path/to/inventory] \
  playbooks/byo/openshift_facts.yml

For Amazon Web Services, see the Overriding Detected IP Addresses and Host Names section.

Now, verify the detected common settings. If they are not what you expect them to be, you can override them.

The Configuring Your Inventory File topic discusses the available Ansible variables in greater detail.

Variable Usage

hostname

  • Resolves to the internal IP address from the instances themselves.

ip

  • The internal IP address of the instance.

public_hostname

  • Resolves to the external IP from hosts outside of the cloud.

  • Provider openshift_public_hostname overrides.

public_ip

  • The externally accessible IP address associated with the instance.

  • openshift_public_ip overrides.

use_openshift_sdn

  • For all clouds but GCE, set to true.

  • openshift_use_openshift_sdn overrides.

Post-Installation Configuration for Cloud Providers

Following the installation process, you can configure OKD for AWS, OpenStack, or GCE.