Chapter 5. Red Hat OpenShift installation planning and considerations 97
Registry
OpenShift can build container images from source code, deploy them, and manage their 
lifecycle. To enable this process, OpenShift provides an internal, integrated registry that can 
be deployed in the OpenShift environment to manage images.
The registry stores images and metadata. For production environments, persistent storage 
must be used for the registry; otherwise, any images that were built or pushed into the registry 
disappear if the pod restarts.
Aggregated logging
One of the Red Hat OpenShift Container Platform optional components is named Red Hat 
OpenShift Container Platform aggregated logging. This component collects and aggregates 
logs from the pods that are running in the Red Hat OpenShift Container Platform cluster and 
/var/log/messages on nodes. This configuration enables Red Hat OpenShift Container 
Platform users to view the logs of projects that they can view by using a web interface.
Red Hat OpenShift Container Platform aggregated logging component is a modified version 
of the ELK stack, which is composed of a few pods that are running on the Red Hat OpenShift 
Container Platform environment:
/SM590000Elasticsearch: An object store where all logs are stored.
/SM590000Kibana: A web UI for Elasticsearch.
/SM590000Curator: Elasticsearch maintenance operations that are performed automatically on a 
per-project basis.
/SM590000Fluentd: Gathers logs from nodes and containers and feeds them to Elasticsearch.
Consider the following basic concepts for aggregated logging:
/SM590000Cluster: A set of Elasticsearch nodes that distribute the workload.
/SM590000Node: A container that is running an instance of Elasticsearch, which is part of the cluster.
/SM590000Index: Collection of documents (container logs).
/SM590000Shards and Replicas: Indexes can be divided into sets of data that contain the primary 
copy of the documents that are stored (primary shards) or backups of that primary copies 
(replica shards). Sharding allows the application to horizontally scale the information and 
distributed/paralellized operations. Replication instead provides HA and also better search 
throughput because searches are also run on replicas.
Red Hat OpenShift Container Platform can gather metrics from kubelet and store the values 
in Heapster. Red Hat OpenShift Container Platform Metrics provide the ability to view CPU, 
memory, and network-based metrics and display the values in the user interface. These 
metrics can allow for the horizontal autoscaling of pods based on parameters that are 
provided by a Red Hat OpenShift Container Platform user. It is important to understand 
capacity planning when metrics are deployed into an Red Hat OpenShift Container Platform 
environment.
Red Hat OpenShift Container Platform metrics is composed by the following pods that are 
running on the Red Hat OpenShift Container Platform environment:
/SM590000Heapster: Heapster scrapes the metrics for CPU, memory, and network usage on every 
Pod. Then, it exports them into Hawkular Metrics.
Note: Using NFS storage as a volume or a persistent volume (or by way of an NAS such 
as Gluster) is not supported for Elasticsearch storage because Lucene relies on file 
system behavior that NFS does not supply. Data corruption and other problems can occur.