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F5 BIG-IP® Router Plug-in - Additional Concepts | Architecture | OpenShift Container Platform 3.5
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F5 BIG-IP® Router Plug-in

Overview

A router is one way to get traffic into the cluster. The F5 BIG-IP® Router plug-in is one of the available router plugins.

The F5 router plug-in is available starting in OpenShift Enterprise 3.0.2.

The F5 router plug-in integrates with an existing F5 BIG-IP® system in your environment. F5 BIG-IP® version 11.4 or newer is required in order to have the F5 iControl REST API. The F5 router supports unsecured, edge terminated, re-encryption terminated, and passthrough terminated routes matching on HTTP vhost and request path.

The F5 router has feature parity with the HAProxy template router, and has additional features over the F5 BIG-IP® support in OpenShift Enterprise 2. Compared with the routing-daemon used in earlier versions, the F5 router additionally supports:

  • path-based routing (using policy rules),

  • re-encryption (implemented using client and server SSL profiles)

  • passthrough of encrypted connections (implemented using an iRule that parses the SNI protocol and uses a data group that is maintained by the F5 router for the servername lookup).

Passthrough routes are a special case: path-based routing is technically impossible with passthrough routes because F5 BIG-IP® itself does not see the HTTP request, so it cannot examine the path. The same restriction applies to the template router; it is a technical limitation of passthrough encryption, not a technical limitation of OpenShift Container Platform.

Routing Traffic to Pods Through the SDN

Because F5 BIG-IP® is external to the OpenShift SDN, a cluster administrator must create a peer-to-peer tunnel between F5 BIG-IP® and a host that is on the SDN, typically an OpenShift Container Platform node host. This ramp node can be configured as unschedulable for pods so that it will not be doing anything except act as a gateway for the F5 BIG-IP® host. It is also possible to configure multiple such hosts and use the OpenShift Container Platform ipfailover feature for redundancy; the F5 BIG-IP® host would then need to be configured to use the ipfailover VIP for its tunnel’s remote endpoint.

F5 Integration Details

The operation of the F5 router is similar to that of the OpenShift Container Platform routing-daemon used in earlier versions. Both use REST API calls to:

  • create and delete pools,

  • add endpoints to and delete them from those pools, and

  • configure policy rules to route to pools based on vhost.

Both also use scp and ssh commands to upload custom TLS/SSL certificates to F5 BIG-IP®.

The F5 router configures pools and policy rules on virtual servers as follows:

  • When a user creates or deletes a route on OpenShift Container Platform, the router creates a pool to F5 BIG-IP® for the route (if no pool already exists) and adds a rule to, or deletes a rule from, the policy of the appropriate vserver: the HTTP vserver for non-TLS routes, or the HTTPS vserver for edge or re-encrypt routes. In the case of edge and re-encrypt routes, the router also uploads and configures the TLS certificate and key. The router supports host- and path-based routes.

    Passthrough routes are a special case: to support those, it is necessary to write an iRule that parses the SNI ClientHello handshake record and looks up the servername in an F5 data-group. The router creates this iRule, associates the iRule with the vserver, and updates the F5 data-group as passthrough routes are created and deleted. Other than this implementation detail, passthrough routes work the same way as other routes.

  • When a user creates a service on OpenShift Container Platform, the router adds a pool to F5 BIG-IP® (if no pool already exists). As endpoints on that service are created and deleted, the router adds and removes corresponding pool members.

  • When a user deletes the route and all endpoints associated with a particular pool, the router deletes that pool.

F5 Native Integration

With native integration of F5 with OpenShift Container Platform, you do not need to configure a ramp node for F5 to be able to reach the pods on the overlay network as created by OpenShift SDN.

Also, only F5 BIG-IP® appliance version 12.x and above works with the native integration presented in this section. You also need sdn-services add-on license for the integration to work properly. For version 11.x, set up a ramp node.

Connection

The F5 appliance can connect to the OpenShift Container Platform cluster via an L3 connection. An L2 switch connectivity is not required between OpenShift Container Platform nodes. On the appliance, you can use multiple interfaces to manage the integration:

  • Management interface - Reaches the web console of the F5 appliance.

  • External interface - Configures the virtual servers for inbound web traffic.

  • Internal interface - Programs the appliance and reaches out to the pods.

F5 and OpenShift Connection Diagram

An F5 controller pod has admin access to the appliance. The F5 image is launched within the OpenShift Container Platform cluster (scheduled on any node) that uses iControl REST APIs to program the virtual servers with policies, and configure the VxLAN device.

Data Flow: Packets to Pods

This section explains how the packets reach the pods, and vice versa. These actions are performed by the F5 controller pod and the F5 appliance, not the user.

When natively integrated, The F5 appliance reaches out to the pods directly using VxLAN encapsulation. This integration works only when OpenShift Container Platform is using openshift-sdn as the network plug-in. The openshift-sdn plug-in employs VxLAN encapsulation for the overlay network that it creates.

To make a successful data path between a pod and the F5 appliance:

  1. F5 needs to encapsulate the VxLAN packet meant for the pods. This requires the sdn-services license add-on. A VxLAN device needs to be created and the pod overlay network needs to be routed through this device.

  2. F5 needs to know the VTEP IP address of the pod, which is the IP address of the node where the pod is located.

  3. F5 needs to know which source-ip to use for the overlay network when encapsulating the packets meant for the pods. This is known as the gateway address.

  4. OpenShift Container Platform nodes need to know where the F5 gateway address is (the VTEP address for the return traffic). This needs to be the internal interface’s address. All nodes of the cluster must learn this automatically.

  5. Since the overlay network is multi-tenant aware, F5 must use a VxLAN ID that is representative of an admin domain, ensuring that all tenants are reachable by the F5. Ensure that F5 encapsulates all packets with a vnid of 0 (the default vnid for the admin namespace in OpenShift Container Platform) by putting an annotation on the manually created hostsubnet - pod.network.openshift.io/fixed-vnid-host: 0.

A ghost hostsubnet is manually created as part of the setup, which fulfills the third and forth listed requirements. When the F5 controller pod is launched, this new ghost hostsubnet is provided so that the F5 appliance can be programmed suitably.

The term ghost hostsubnet is used because it suggests that a subnet has been given to a node of the cluster. However, in reality, it is not a real node of the cluster. It is hijacked by an external appliance.

The first requirement is fulfilled by the F5 controller pod once it is launched. The second requirement is also fulfilled by the F5 controller pod, but it is an ongoing process. For each new node that is added to the cluster, the controller pod creates an entry in the VxLAN device’s VTEP FDB. The controller pod needs access to the nodes resource in the cluster, which you can accomplish by giving the service account appropriate privileges. Use the following command:

$ oc adm policy add-cluster-role-to-user system:sdn-reader system:serviceaccount:default:router

Data Flow from the F5 Host

These actions are performed by the F5 controller pod and the F5 appliance, not the user.

  1. The destination pod is identified by the F5 virtual server for a packet.

  2. VxLAN dynamic FDB is looked up with pod’s IP address. If a MAC address is found, go to step 5.

  3. Flood all entries in the VTEP FDB with ARP requests seeking the pod’s MAC address.

  4. One of the nodes (VTEP) will respond, confirming that it is the one where the pod is located. An entry is made into the VxLAN dynamic FDB with the pod’s MAC address and the VTEP to be used as the value.

  5. Encap an IP packet with VxLAN headers, where the MAC of the pod and the VTEP of the node is given as values from the VxLAN dynamic FDB.

  6. Calculate the VTEP’s MAC address by sending out an ARP or checking the host’s neighbor cache.

  7. Deliver the packet through the F5 host’s internal address.

Data Flow: Return Traffic to the F5 Host

These actions are performed by the F5 controller pod and the F5 appliance, not the user.

  1. The pod sends back a packet with the destination as the F5 host’s VxLAN gateway address.

  2. The openvswitch at the node determines that the VTEP for this packet is the F5 host’s internal interface address. This is learned from the ghost hostsubnet creation.

  3. A VxLAN packet is sent out to the internal interface of the F5 host.

During the entire data flow, the VNID is pre-fixed to be 0 to bypass multi-tenancy.