Chapter 1. Monitoring overview
1.1. About OpenShift Container Platform monitoring
OpenShift Container Platform includes a preconfigured, preinstalled, and self-updating monitoring stack that provides monitoring for core platform components. You also have the option to enable monitoring for user-defined projects.
A cluster administrator can configure the monitoring stack with the supported configurations. OpenShift Container Platform delivers monitoring best practices out of the box.
A set of alerts are included by default that immediately notify administrators about issues with a cluster. Default dashboards in the OpenShift Container Platform web console include visual representations of cluster metrics to help you to quickly understand the state of your cluster. With the OpenShift Container Platform web console, you can view and manage metrics, alerts, and review monitoring dashboards.
In the Observe section of OpenShift Container Platform web console, you can access and manage monitoring features such as metrics, alerts, monitoring dashboards, and metrics targets.
After installing OpenShift Container Platform, cluster administrators can optionally enable monitoring for user-defined projects. By using this feature, cluster administrators, developers, and other users can specify how services and pods are monitored in their own projects. As a cluster administrator, you can find answers to common problems such as user metrics unavailability and high consumption of disk space by Prometheus in Troubleshooting monitoring issues.
1.2. Understanding the monitoring stack
The OpenShift Container Platform monitoring stack is based on the Prometheus open source project and its wider ecosystem. The monitoring stack includes the following:
Default platform monitoring components. A set of platform monitoring components are installed in the
openshift-monitoringproject by default during an OpenShift Container Platform installation. This provides monitoring for core cluster components including Kubernetes services. The default monitoring stack also enables remote health monitoring for clusters.These components are illustrated in the Installed by default section in the following diagram.
-
Components for monitoring user-defined projects. After optionally enabling monitoring for user-defined projects, additional monitoring components are installed in the
openshift-user-workload-monitoringproject. This provides monitoring for user-defined projects. These components are illustrated in the User section in the following diagram.
1.2.1. Default monitoring components
By default, the OpenShift Container Platform 4.17 monitoring stack includes these components:
| Component | Description |
|---|---|
| Cluster Monitoring Operator | The Cluster Monitoring Operator (CMO) is a central component of the monitoring stack. It deploys, manages, and automatically updates Prometheus and Alertmanager instances, Thanos Querier, Telemeter Client, and metrics targets. The CMO is deployed by the Cluster Version Operator (CVO). |
| Prometheus Operator |
The Prometheus Operator (PO) in the |
| Prometheus | Prometheus is the monitoring system on which the OpenShift Container Platform monitoring stack is based. Prometheus is a time-series database and a rule evaluation engine for metrics. Prometheus sends alerts to Alertmanager for processing. |
| Metrics Server |
The Metrics Server component (MS in the preceding diagram) collects resource metrics and exposes them in the |
| Alertmanager | The Alertmanager service handles alerts received from Prometheus. Alertmanager is also responsible for sending the alerts to external notification systems. |
| kube-state-metrics agent | The kube-state-metrics exporter agent (KSM in the preceding diagram) converts Kubernetes objects to metrics that Prometheus can use. |
| monitoring-plugin | The monitoring-plugin dynamic plugin component deploys the monitoring pages in the Observe section of the OpenShift Container Platform web console. You can use Cluster Monitoring Operator config map settings to manage monitoring-plugin resources for the web console pages. |
| openshift-state-metrics agent | The openshift-state-metrics exporter (OSM in the preceding diagram) expands upon kube-state-metrics by adding metrics for OpenShift Container Platform-specific resources. |
| node-exporter agent | The node-exporter agent (NE in the preceding diagram) collects metrics about every node in a cluster. The node-exporter agent is deployed on every node. |
| Thanos Querier | Thanos Querier aggregates and optionally deduplicates core OpenShift Container Platform metrics and metrics for user-defined projects under a single, multi-tenant interface. |
| Telemeter Client | Telemeter Client sends a subsection of the data from platform Prometheus instances to Red Hat to facilitate Remote Health Monitoring for clusters. |
All of the components in the monitoring stack are monitored by the stack and are automatically updated when OpenShift Container Platform is updated.
All components of the monitoring stack use the TLS security profile settings that are centrally configured by a cluster administrator. If you configure a monitoring stack component that uses TLS security settings, the component uses the TLS security profile settings that already exist in the tlsSecurityProfile field in the global OpenShift Container Platform apiservers.config.openshift.io/cluster resource.
1.2.2. Default monitoring targets
In addition to the components of the stack itself, the default monitoring stack monitors additional platform components.
The following are examples of monitoring targets:
- CoreDNS
- etcd
- HAProxy
- Image registry
- Kubelets
- Kubernetes API server
- Kubernetes controller manager
- Kubernetes scheduler
- OpenShift API server
- OpenShift Controller Manager
- Operator Lifecycle Manager (OLM)
- The exact list of targets can vary depending on your cluster capabilities and installed components.
- Each OpenShift Container Platform component is responsible for its monitoring configuration. For problems with the monitoring of an OpenShift Container Platform component, open a Jira issue against that component, not against the general monitoring component.
Other OpenShift Container Platform framework components might be exposing metrics as well. For details, see their respective documentation.
Additional resources
1.2.3. Components for monitoring user-defined projects
OpenShift Container Platform includes an optional enhancement to the monitoring stack that enables you to monitor services and pods in user-defined projects. This feature includes the following components:
| Component | Description |
|---|---|
| Prometheus Operator |
The Prometheus Operator (PO) in the |
| Prometheus | Prometheus is the monitoring system through which monitoring is provided for user-defined projects. Prometheus sends alerts to Alertmanager for processing. |
| Thanos Ruler | The Thanos Ruler is a rule evaluation engine for Prometheus that is deployed as a separate process. In OpenShift Container Platform , Thanos Ruler provides rule and alerting evaluation for the monitoring of user-defined projects. |
| Alertmanager | The Alertmanager service handles alerts received from Prometheus and Thanos Ruler. Alertmanager is also responsible for sending user-defined alerts to external notification systems. Deploying this service is optional. |
The components in the preceding table are deployed after monitoring is enabled for user-defined projects.
All of these components are monitored by the stack and are automatically updated when OpenShift Container Platform is updated.
1.2.4. Monitoring targets for user-defined projects
When monitoring is enabled for user-defined projects, you can monitor:
- Metrics provided through service endpoints in user-defined projects.
- Pods running in user-defined projects.
1.2.5. Understanding the monitoring stack in high-availability clusters
By default, in multi-node clusters, the following components run in high-availability (HA) mode to prevent data loss and service interruption:
- Prometheus
- Alertmanager
- Thanos Ruler
- Thanos Querier
- Metrics Server
- Monitoring plugin
The component is replicated across two pods, each running on a separate node. This means that the monitoring stack can tolerate the loss of one pod.
- Prometheus in HA mode
- Both replicas independently scrape the same targets and evaluate the same rules.
- The replicas do not communicate with each other. Therefore, data might differ between the pods.
- Alertmanager in HA mode
- The two replicas synchronize notification and silence states with each other. This ensures that each notification is sent at least once.
- If the replicas fail to communicate or if there is an issue on the receiving side, notifications are still sent, but they might be duplicated.
Prometheus, Alertmanager, and Thanos Ruler are stateful components. To ensure high availability, you must configure them with persistent storage.
1.3. Glossary of common terms for OpenShift Container Platform monitoring
This glossary defines common terms that are used in OpenShift Container Platform architecture.
- Alertmanager
- Alertmanager handles alerts received from Prometheus. Alertmanager is also responsible for sending the alerts to external notification systems.
- Alerting rules
- Alerting rules contain a set of conditions that outline a particular state within a cluster. Alerts are triggered when those conditions are true. An alerting rule can be assigned a severity that defines how the alerts are routed.
- Cluster Monitoring Operator
- The Cluster Monitoring Operator (CMO) is a central component of the monitoring stack. It deploys and manages Prometheus instances such as, the Thanos Querier, the Telemeter Client, and metrics targets to ensure that they are up to date. The CMO is deployed by the Cluster Version Operator (CVO).
- Cluster Version Operator
- The Cluster Version Operator (CVO) manages the lifecycle of cluster Operators, many of which are installed in OpenShift Container Platform by default.
- config map
-
A config map provides a way to inject configuration data into pods. You can reference the data stored in a config map in a volume of type
ConfigMap. Applications running in a pod can use this data. - Container
- A container is a lightweight and executable image that includes software and all its dependencies. Containers virtualize the operating system. As a result, you can run containers anywhere from a data center to a public or private cloud as well as a developer’s laptop.
- custom resource (CR)
- A CR is an extension of the Kubernetes API. You can create custom resources.
- etcd
- etcd is the key-value store for OpenShift Container Platform, which stores the state of all resource objects.
- Fluentd
Fluentd is a log collector that resides on each OpenShift Container Platform node. It gathers application, infrastructure, and audit logs and forwards them to different outputs.
NoteFluentd is deprecated and is planned to be removed in a future release. Red Hat provides bug fixes and support for this feature during the current release lifecycle, but this feature no longer receives enhancements. As an alternative to Fluentd, you can use Vector instead.
- Kubelets
- Runs on nodes and reads the container manifests. Ensures that the defined containers have started and are running.
- Kubernetes API server
- Kubernetes API server validates and configures data for the API objects.
- Kubernetes controller manager
- Kubernetes controller manager governs the state of the cluster.
- Kubernetes scheduler
- Kubernetes scheduler allocates pods to nodes.
- labels
- Labels are key-value pairs that you can use to organize and select subsets of objects such as a pod.
- Metrics Server
-
The Metrics Server monitoring component collects resource metrics and exposes them in the
metrics.k8s.ioMetrics API service for use by other tools and APIs, which frees the core platform Prometheus stack from handling this functionality. - node
- A worker machine in the OpenShift Container Platform cluster. A node is either a virtual machine (VM) or a physical machine.
- Operator
- The preferred method of packaging, deploying, and managing a Kubernetes application in an OpenShift Container Platform cluster. An Operator takes human operational knowledge and encodes it into software that is packaged and shared with customers.
- Operator Lifecycle Manager (OLM)
- OLM helps you install, update, and manage the lifecycle of Kubernetes native applications. OLM is an open source toolkit designed to manage Operators in an effective, automated, and scalable way.
- Persistent storage
- Stores the data even after the device is shut down. Kubernetes uses persistent volumes to store the application data.
- Persistent volume claim (PVC)
- You can use a PVC to mount a PersistentVolume into a Pod. You can access the storage without knowing the details of the cloud environment.
- pod
- The pod is the smallest logical unit in Kubernetes. A pod is comprised of one or more containers to run in a worker node.
- Prometheus
- Prometheus is the monitoring system on which the OpenShift Container Platform monitoring stack is based. Prometheus is a time-series database and a rule evaluation engine for metrics. Prometheus sends alerts to Alertmanager for processing.
- Prometheus Operator
-
The Prometheus Operator (PO) in the
openshift-monitoringproject creates, configures, and manages platform Prometheus and Alertmanager instances. It also automatically generates monitoring target configurations based on Kubernetes label queries. - Silences
- A silence can be applied to an alert to prevent notifications from being sent when the conditions for an alert are true. You can mute an alert after the initial notification, while you work on resolving the underlying issue.
- storage
- OpenShift Container Platform supports many types of storage, both for on-premise and cloud providers. You can manage container storage for persistent and non-persistent data in an OpenShift Container Platform cluster.
- Thanos Ruler
- The Thanos Ruler is a rule evaluation engine for Prometheus that is deployed as a separate process. In OpenShift Container Platform, Thanos Ruler provides rule and alerting evaluation for the monitoring of user-defined projects.
- Vector
- Vector is a log collector that deploys to each OpenShift Container Platform node. It collects log data from each node, transforms the data, and forwards it to configured outputs.
- web console
- A user interface (UI) to manage OpenShift Container Platform.
