Routes

An OKD route exposes a service at a host name, such as 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 OKD node that is running the OKD 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 OKD administrator can deploy routers to nodes in an OKD cluster, which enable routes created by developers to be used by external clients. The routing layer in OKD is pluggable, and several 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, OKD 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.

OKD 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:

For a secure connection to be established, a cipher common to the client and server must be negotiated. As time goes on, new, more secure ciphers become available and are integrated into client software. As older clients become obsolete, the older, less secure ciphers can be dropped. By default, the router supports a broad range of commonly available clients. The router can be configured to use a selected set of ciphers that support desired clients and do not include the less secure ciphers.

See the Available router plug-ins section for the verified available router plug-ins.

Instructions on deploying these routers are available in Deploying a Router.

Implementing sticky sessions is up to the underlying router configuration. The template router plug-in provides the service name and namespace to the underlying implementation. This can be used for more advanced configuration, such as implementing stick-tables that synchronize between a set of peers.

Sticky sessions ensure that all traffic from a user’s session go to the same pod, creating a better user experience. While satisfying the user’s requests, the pod caches data, which can be used in subsequent requests. For example, for a cluster with five back-end pods and two load-balanced routers, you can ensure that the same pod receives the web traffic from the same web browser regardless of the router that handles it.

While returning routing traffic to the same pod is desired, it cannot be guaranteed. However, you can use HTTP headers to set a cookie to determine the pod used in the last connection. When the user sends another request to the application the browser re-sends the cookie and the router knows where to send the traffic.

Cluster administrators can turn off stickiness for passthrough routes separately from other connections, or turn off stickiness entirely.

By default, sticky sessions for passthrough routes are implemented using the source load-balancing strategy. However, the roundrobin load-balancing strategy is the default when there are active services with weights greater than 1. You can change the default for all passthrough routes by using the ROUTER_LOAD_BALANCE_ALGORITHM environment variable, and for individual routes by using the haproxy.router.openshift.io/balance route specific annotation.

Other types of routes use the leastconn load-balancing strategy by default, which can be changed by using the ROUTER_LOAD_BALANCE_ALGORITHM environment variable. It can be changed for individual routes by using the haproxy.router.openshift.io/balance route specific annotation.

In addition, the template router plug-in provides the service name and namespace to the underlying implementation. This can be used for more advanced configuration such as implementing stick-tables that synchronize between a set of peers.

Specific configuration for this router implementation is stored in the haproxy-config.template file located in the /var/lib/haproxy/conf directory of the router container. The file may be customized.

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

For example:

Router timeout variables

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)

When a route has multiple endpoints, HAProxy distributes requests to the route among the endpoints based on the selected load-balancing strategy. This applies when no persistence information is available, such as on the first request in a session.

The strategy can be one of the following:

The ROUTER_TCP_BALANCE_SCHEME environment variable sets the default strategy for passthorugh routes. The ROUTER_LOAD_BALANCE_ALGORITHM environment variable sets the default strategy for the router for the remaining routes. A route specific annotation, haproxy.router.openshift.io/balance, can be used to control specific routes.

By default, when a host does not resolve to a route in a HTTPS or TLS SNI request, the default certificate is returned to the caller as part of the 503 response. This exposes the default certificate and can pose security concerns because the wrong certificate is served for a site. The HAProxy strict-sni option to bind suppresses use of the default certificate.

The ROUTER_STRICT_SNI environment variable controls bind processing. When set to true or TRUE, strict-sni is added to the HAProxy bind. The default setting is false.

The option can be set when the router is created or added later.

This sets ROUTER_STRICT_SNI=true.

Each client (for example, Chrome 30, or Java8) includes a suite of ciphers used to securely connect with the router. The router must have at least one of the ciphers for the connection to be complete:

See the Security/Server Side TLS reference guide for more information.

The router defaults to the intermediate profile. You can select a different profile using the --ciphers option when creating a route, or by changing the ROUTER_CIPHERS environment variable with the values modern, intermediate, or old for an existing router. Alternatively, a set of ":" separated ciphers can be provided. The ciphers must be from the set displayed by:

In order for services to be exposed externally, an OKD 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 host name: an older one and a newer one. If someone else has a route for the same host name that they created between when you created the other two routes, then if you delete your older route, your claim to the host name will no longer be in effect. The other namespace now claims the host name and your claim is lost.

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

The following example shows the OKD-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.

In OKD, 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 OKD 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.

A route is usually associated with one service through the to: token with kind: Service. All of the requests to the route are handled by endpoints in the service based on the load balancing strategy.

It is possible to have as many as four services supporting the route. The portion of requests that are handled by each service is governed by the service weight.

The first service is entered using the to: token as before, and up to three additional services can be entered using the alternateBackend: token. Each service must be kind: Service which is the default.

Each service has a weight associated with it. The portion of requests handled by the service is weight / sum_of_all_weights. When a service has more than one endpoint, the service’s weight is distributed among the endpoints with each endpoint getting at least 1. If the service weight is 0 each of the service’s endpoints will get 0.

The weight must be in the range 0-256. The default is 1. When the weight is 0 no requests are passed to the service. If all services have weight 0, requests are returned with a 503 error. When a service has no endpoints, the weight is effectively 0.

When using alternateBackends also use the roundrobin load balancing strategy to ensure requests are distributed as expected to the services based on weight. roundrobin can be set for a route using a route annotation, or for the router in general using an environment variable.

The following is an example route configuration using alternate backends for A/B deployments.

Using environment variables, 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

You can restrict access to a route to a select set of IP addresses by adding the haproxy.router.openshift.io/ip_whitelist annotation on the route. The whitelist is a space-separated list of IP addresses and/or CIDRs for the approved source addresses. Requests from IP addresses that are not in the whitelist are dropped.

Some examples:

When editing a route, add the following annotation to define the desired source IP’s. Alternatively, use oc annotate route <name>.

Allow only one specific IP address:

Allow several IP addresses:

Allow an IP CIDR network:

Allow mixed IP addresses and IP CIDR networks:

A wildcard policy allows a user to define a route that covers all hosts within a domain (when the router is configured to allow it). A route can specify a wildcard policy as part of its configuration using the wildcardPolicy field. Any routers run with a policy allowing wildcard routes will expose the route appropriately based on the wildcard policy.

Learn how to configure HAProxy routers to allow wildcard routes.

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.

A router can be configured to deny or allow a specific subset of domains from the host names in a route using the ROUTER_DENIED_DOMAINS and ROUTER_ALLOWED_DOMAINS environment variables.

The domains in the list of denied domains take precedence over the list of allowed domains. Meaning OKD first checks the deny list (if applicable), and if the host name is not in the list of denied domains, it then checks the list of allowed domains. However, the list of allowed domains is more restrictive, and ensures that the router only admits routes with hosts that belong to that list.

For example, to deny the [*.]open.header.test, [*.]openshift.org and [*.]block.it routes for the myrouter route:

This means that myrouter will admit the following based on the route’s name:

However, myrouter will deny the following:

Alternatively, to block any routes where the host name is not set to [*.]stickshift.org or [*.]kates.net:

This means that the myrouter router will admit:

However, myrouter will deny the following:

To implement both scenarios, run:

This will allow any routes where the host name is set to [*.]openshift.org or [*.]kates.net, and not allow any routes where the host name is set to [*.]ops.openshift.org or [*.]metrics.kates.net.

Therefore, the following will be denied:

However, the following will be allowed:

Hosts and subdomains are owned by the namespace of the route that first makes the claim. Other routes created in the namespace can make claims on the subdomain. All other namespaces are prevented from making claims on the claimed hosts and subdomains. The namespace that owns the host also owns all paths associated with the host, for example www.abc.xyz/path1.

For example, if the host www.abc.xyz is not claimed by any route. Creating route r1 with host www.abc.xyz in namespace ns1 makes namespace ns1 the owner of host www.abc.xyz and subdomain abc.xyz for wildcard routes. If another namespace, ns2, tries to create a route with say a different path www.abc.xyz/path1/path2, it would fail because a route in another namespace (ns1 in this case) owns that host.

With wildcard routes the namespace that owns the subdomain owns all hosts in the subdomain. If a namespace owns subdomain abc.xyz as in the above example, another namespace cannot claim z.abc.xyz.

By disabling the namespace ownership rules, you can disable these restrictions and allow hosts (and subdomains) to be claimed across namespaces.

For example, with ROUTER_DISABLE_NAMESPACE_OWNERSHIP_CHECK=true, if namespace ns1 creates the oldest route r1 www.abc.xyz, it owns only the hostname (+ path). Another namespace can create a wildcard route even though it does not have the oldest route in that subdomain (abc.xyz) and we could potentially have other namespaces claiming other non-wildcard overlapping hosts (for example, foo.abc.xyz, bar.abc.xyz, baz.abc.xyz) and their claims would be granted.

Any other namespace (for example, ns2) can now create a route r2 www.abc.xyz/p1/p2, and it would be admitted. Similarly another namespace (ns3) can also create a route wildthing.abc.xyz with a subdomain wildcard policy and it can own the wildcard.

As this example demonstrates, the policy ROUTER_DISABLE_NAMESPACE_OWNERSHIP_CHECK=true is more lax and allows claims across namespaces. The only time the router would reject a route with the namespace ownership disabled is if the host+path is already claimed.

For example, if a new route rx tries to claim www.abc.xyz/p1/p2, it would be rejected as route r2 owns that host+path combination. This is true whether route rx is in the same namespace or other namespace since the exact host+path is already claimed.

This feature can be set during router creation or by setting an environment variable in the router’s deployment configuration.