OpenShift Concepts TODEPLETE
Internal
Overview
OpenShift is supported anywhere RHEL is: bare metal, virtualized infrastructure (Red Hat Virtualization, vSphere, Hyper-V), OpenStack platform, public cloud providers (Amazon, Google, Azure). It runs on RHEL and Red Hat Atomic.
OpenShift Hosts
Master
A master is a RHEL or Red Hat Atomic host that orchestrates and schedules resources. It maintains the state of the OpenShift environment. Multiple masters can be present to insure HA.
The master provides the single API all tooling clients must interact with.
The access is protected via fine-grained role-based access control (RBAC).
The master monitors application health via user-defined pod probes. It handles restarting pods that failed probes automatically. Pods that fail too often are marked as "failing" and are temporarily not restarted. The OpenShift service layer sends traffic only to healthy pods.
Node
A node is a RHEL or Red Hat Atomic Host where applications run inside containers. Nodes are orchestrated by masters. The node daemon runs on node.
Container
All application instances run inside containers on the nodes. For more details, see Docker Containers.
The node Daemon
Pod
Pod Probe
Users can configure pod probes for liveness or readiness.
Storage
Volume
etcd
Scheduler
Docker Registry
OpenShift contains an integrated Docker registry. Users push images into registry and whenever a new image is stored in the registry, the registry notifies OpenShift about it and passes along image information such as the namespace, the name and the image metadata.
Service
Routing Layer
The routing layer cooperates with the service layer. It runs in pods and it provides automated load balancing to pods, and routing around unhealthy pods. The routing layer is pluggable and extensible.
API
Label
Selector
Replication Controller
Networking
Router
The router component routes external requests to applications inside the OpenShift environment. The router is the ingress point for all traffic destined for OpenShift services. Runs in a container.
Route
A route is a way to expose a service by giving it an externally reachable hostname. A route is a mapping of an FQDN and path to the endpoints of a service. Each route consist of a route name, a service selector and an optional security configuration.
Projects
Projects allows groups of users to work together, define ownership of resources and manage resources. The project restricts and tracks use of resources with quotas and limits. A project is a Kubernetes namespace with additional annotations.
A project lets a community of users to organize and manage their content in isolation from other communities.
Each project has its own set of:
Objects
The objects include pods, services, replication controllers, etc.
User Accounts
Are created upon login or via the API and represented with the User object.
System Users
These users are created automatically when the infrastructure is defined, for the purpose of enabling the infrastructure to interact with the API securely. The cluster administrator has access to everything.
Service Accounts
Non-human users that act automatically with designated access to objects in their projects or other projects.
Group
Policies
Constraints
Constraints are quotas for each kind of object that can be limited.
Resources
- cpu, requests.cpu
- memory, requests.memory
- limits.cpu
- memory.cpu
- pods
- replicationcontrollers
- resourcequotas
- services
- secrets
- configmaps
- persistentvolumeclaims
- openshif.io/imagestreams
Resource Quota
ResourceQuota object enumerates hard resource usage limits per project.
ClusterResourceQuotaobject enumerates hard resource usage limits across the cluster.