Routes

An OpenShift Container Platform route exposes a service at a host name, like www.example.com, so that external clients can reach it by name.

DNS resolution for a host name is handled separately from routing. Your administrator may have configured a DNS wildcard entry that will resolve to the OpenShift Container Platform node that is running the OpenShift Container Platform router. If you are using a different host name you may need to modify its DNS records independently to resolve to the node that is running the router.

Each route consists of a name (limited to 63 characters), a service selector, and an optional security configuration.

An OpenShift Container Platform administrator can deploy routers to nodes in an OpenShift Container Platform cluster, which enable routes created by developers to be used by external clients. The routing layer in OpenShift Container Platform is pluggable, and two available router plug-ins are provided and supported by default.

A router uses the service selector to find the service and the endpoints backing the service. When both router and service provide load balancing, OpenShift Container Platform uses the router load balancing. A router detects relevant changes in the IP addresses of its services and adapts its configuration accordingly. This is useful for custom routers to communicate modifications of API objects to an external routing solution.

The path of a request starts with the DNS resolution of a host name to one or more routers. The suggested method is to define a cloud domain with a wildcard DNS entry pointing to one or more virtual IP (VIP) addresses backed by multiple router instances. Routes using names and addresses outside the cloud domain require configuration of individual DNS entries.

When there are fewer VIP addresses than routers, the routers corresponding to the number of addresses are active and the rest are passive. A passive router is also known as a hot-standby router. For example, with two VIP addresses and three routers, you have an "active-active-passive" configuration. See High Availability for more information on router VIP configuration.

Routes can be sharded among the set of routers. Administrators can set up sharding on a cluster-wide basis and users can set up sharding for the namespace in their project. Sharding allows the operator to define multiple router groups. Each router in the group serves only a subset of traffic.

OpenShift Container Platform routers provide external host name mapping and load balancing of service end points over protocols that pass distinguishing information directly to the router; the host name must be present in the protocol in order for the router to determine where to send it.

Router plug-ins assume they can bind to host ports 80 (HTTP) and 443 (HTTPS), by default. This means that routers must be placed on nodes where those ports are not otherwise in use. Alternatively, a router can be configured to listen on other ports by setting the ROUTER_service_HTTP_PORT and ROUTER_service_HTTPS_PORT environment variables.

Because a router binds to ports on the host node, only one router listening on those ports can be on each node if the router uses host networking (the default). Cluster networking is configured such that all routers can access all pods in the cluster.

Routers support the following protocols:

The following router plug-ins are provided and supported in OpenShift Container Platform. Instructions on deploying these routers are available in Deploying a Router.

For all the items outlined in this section, you can set environment variables on the deployment config for the router to alter its configuration, or use the oc set env command:

For example:

TimeUnits are represented by a number followed by the unit: us (microseconds), ms (milliseconds, default), s (seconds), m (minutes), h *(hours), d (days). The regular expression is: [1-9][0-9](us\|ms\|s\|m\|h\|d)

In order for services to be exposed externally, an OpenShift Container Platform route allows you to associate a service with an externally-reachable host name. This edge host name is then used to route traffic to the service.

When multiple routes from different namespaces claim the same host, the oldest route wins and claims it for the namespace. If additional routes with different path fields are defined in the same namespace, those paths are added. If multiple routes with the same path are used, the oldest takes priority.

A consequence of this behavior is that if you have two routes for a hostname: an older one and a newer one. If someone else has a route for the same hostname that they created between when you created the other two routes, then if you delete your older route, your claim to the hostname will no longer be in effect. The other namespace now claims the hostname and your claim is lost.

If a host name is not provided as part of the route definition, then OpenShift Container Platform automatically generates one for you. The generated host name is of the form:

The following example shows the OpenShift Container Platform-generated host name for the above configuration of a route without a host added to a namespace mynamespace:

A cluster administrator can also customize the suffix used as the default routing subdomain for their environment.

Routes can be either secured or unsecured. Secure routes provide the ability to use several types of TLS termination to serve certificates to the client. Routers support edge, passthrough, and re-encryption termination.

Unsecured routes are simplest to configure, as they require no key or certificates, but secured routes offer security for connections to remain private.

A secured route is one that specifies the TLS termination of the route. The available types of termination are described below.

Path based routes specify a path component that can be compared against a URL (which requires that the traffic for the route be HTTP based) such that multiple routes can be served using the same hostname, each with a different path. Routers should match routes based on the most specific path to the least; however, this depends on the router implementation. The following table shows example routes and their accessibility:

Secured routes specify the TLS termination of the route and, optionally, provide a key and certificate(s).

Secured routes can use any of the following three types of secure TLS termination.

Edge Termination

With edge termination, TLS termination occurs at the router, prior to proxying traffic to its destination. TLS certificates are served by the front end of the router, so they must be configured into the route, otherwise the router’s default certificate will be used for TLS termination.

Because TLS is terminated at the router, connections from the router to the endpoints over the internal network are not encrypted.

Edge-terminated routes can specify an insecureEdgeTerminationPolicy that enables traffic on insecure schemes (HTTP) to be disabled, allowed or redirected. The allowed values for insecureEdgeTerminationPolicy are: None or empty (for disabled), Allow or Redirect. The default insecureEdgeTerminationPolicy is to disable traffic on the insecure scheme. A common use case is to allow content to be served via a secure scheme but serve the assets (example images, stylesheets and javascript) via the insecure scheme.

Passthrough Termination

With passthrough termination, encrypted traffic is sent straight to the destination without the router providing TLS termination. Therefore no key or certificate is required.

The destination pod is responsible for serving certificates for the traffic at the endpoint. This is currently the only method that can support requiring client certificates (also known as two-way authentication).

Re-encryption Termination

Re-encryption is a variation on edge termination where the router terminates TLS with a certificate, then re-encrypts its connection to the endpoint which may have a different certificate. Therefore the full path of the connection is encrypted, even over the internal network. The router uses health checks to determine the authenticity of the host.

In OpenShift Container Platform, each route can have any number of labels in its metadata field. A router uses selectors (also known as a selection expression) to select a subset of routes from the entire pool of routes to serve. A selection expression can also involve labels on the route’s namespace. The selected routes form a router shard. You can create and modify router shards independently from the routes, themselves.

This design supports traditional sharding as well as overlapped sharding. In traditional sharding, the selection results in no overlapping sets and a route belongs to exactly one shard. In overlapped sharding, the selection results in overlapping sets and a route can belong to many different shards. For example, a single route may belong to a SLA=high shard (but not SLA=medium or SLA=low shards), as well as a geo=west shard (but not a geo=east shard).

Another example of overlapped sharding is a set of routers that select based on namespace of the route:

Both router-2 and router-3 serve routes that are in the namespaces Q*, R*, S*, T*. To change this example from overlapped to traditional sharding, we could change the selection of router-2 to K* — P*, which would eliminate the overlap.

When routers are sharded, a given route is bound to zero or more routers in the group. The route binding ensures uniqueness of the route across the shard. Uniqueness allows secure and non-secure versions of the same route to exist within a single shard. This implies that routes now have a visible life cycle that moves from created to bound to active.

In the sharded environment the first route to hit the shard reserves the right to exist there indefinitely, even across restarts.

During a green/blue deployment a route may be be selected in multiple routers. An OpenShift Container Platform application administrator may wish to bleed traffic from one version of the application to another and then turn off the old version.

Sharding can be done by the administrator at a cluster level and by the user at a project/namespace level. When namespace labels are used, the service account for the router must have cluster-reader permission to permit the router to access the labels in the namespace.

Using environment variables as defined in Configuration Parameters, a router can set the default options for all the routes it exposes. An individual route can override some of these defaults by providing specific configurations in its annotations.

Route Annotations

For all the items outlined in this section, you can set annotations on the route definition for the route to alter its configuration

The route status field is only set by routers. If changes are made to a route so that a router no longer serves a specific route, the status becomes stale. The routers do not clear the route status field. To remove the stale entries in the route status, use the clear-route-status script.