Enabling and configuring TCP routing in Cloud Foundry

TCP routing overview
TCP routing architecture
Prerequisites for activating TCP routing
Enable TCP routing
- TLS for TCP Routing
Configure TCP routing after deploying Cloud Foundry
- Configure Cloud Foundry with your TCP Domain
- Configure a quota for TCP routes
Create a TCP route
Modify TCP port reservations
Deactivate TCP routing

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You can enable TCP routing in Cloud Foundry. Learn about TCP routing and go through the steps of enabling and configuring it.

TCP routing overview

You can use TCP routing to run apps that serve requests on non-HTTP TCP protocols. You can use TCP routing to comply with regulatory requirements to stop TLS as close to apps as possible so that packets are not decrypted before reaching the app level.

TCP routing architecture

The following diagram shows the layers of network address translation that occur in Cloud Foundry Application Runtime in support of TCP routing.

Route Ports

The following example workflow ships with route ports, back end ports, and app ports:

You create a TCP route for your app based on a TCP domain and a route port, and map this route to one or more apps. See Create a Route in Configuring Routes and Domains.
Clients make requests to the route. DNS resolves the domain name to the load balancer.
The load balancer listens on the port and forwards requests for the domain to the TCP routers. The load balancer must listen on a range of ports to support multiple TCP route creation. Additionally, Cloud Foundry must be configured with this range, so that the platform knows which ports can be reserved when you create TCP routes.
The TCP router can be dynamically configured to listen on the port when the route is mapped to an app. The domain the request was originally sent to is no longer relevant to the routing of the request to the app. The TCP router keeps a dynamically updated record of the back ends for each route port. The back ends represent instances of an app mapped to the route. The TCP router chooses a back end using a round-robin load balancing algorithm for each new TCP connection from a client. Because the TCP router is protocol-agnostic, it does not recognize individual requests, only TCP connections. All client requests transit the same connection to the selected back end until the client or back end closes the connection. Each subsequent connection initiates the selection of a back end.
Because containers each have their own private network, the TCP router does not have direct access to app containers. When a container is created for an app instance, a port on the Diego Cell VM is randomly chosen and iptables are configured to forward requests for this port to the internal interface on the app container. The TCP router then receives a mapping of the route port to the Diego Cell IP and port.
By default, the Diego Cell only routes requests to port 8080, the app port, on the app container internal interface. The app port is the port on which apps must listen. Developers can use the Cloud Controller API to update the ports an app can receive requests on.

For more information, see Configuring Apps to Listen on Custom Ports (Beta).

Prerequisites for activating TCP routing

Note: If you have mutual TLS app identity verification enabled, app containers accept incoming communication only from the Gorouter. This disables TCP routing. For more information, see TLS to Apps and Other Back End Services in HTTP Routing.

Before you activate TCP routing, you must set up networking requirements.

To set up networking requirements:

Choose a domain from which you can create TCP routes for your apps. For example, create a domain which is similar to your app domain but prefixed by the TCP subdomain, such as tcp.APP-DOMAIN.com, where APP-DOMAIN is the name of your app domain.
Configure DNS to resolve this domain name to the IP address of a highly available load balancer that can forward traffic for the domain to the TCP routers. For more information, see Domains in Configuring Routes and Domains. If you are operating an environment that does not require high availability, configure DNS to resolve the TCP domain name you have chosen directly to a single instance of the TCP router.
(Optional) Choose IP addresses for the TCP routers and configure your load balancer to forward requests for the domain you chose in the first step above to these addresses. Skip this step if you have configured DNS to resolve the TCP domain name to an instance of the TCP router. Configure these IPs as your static IPs in your deployment manifest.
(Optional) Decide how many TCP routes you want to support. For each TCP route, you must reserve a port. Configure your load balancer to forward the range of ports to the TCP routers. Skip this step if you have configured DNS to resolve the TCP domain name to an instance of the TCP router. For more information about configuring port reservations, see Modify TCP Port Reservations.
(Optional) Configure the routing_api.router_groups manifest property with the same range of ports that you configured your load balancer with in the previous step:
```
routing_api.router_groups:
− name: default-tcp
  reservable_ports: CONFIGURED-PORTS
  type: tcp
```
Where CONFIGURED-PORTS is the range of ports that you configured your load balancer with in the previous step.

For more information, see the Routing Release repository in GitHub.

To modify the ports after you have deployed, see Modify TCP Port Reservations.

TLS for TCP Routing

Starting with cf-deployment v43.0.0, Cloud Foundry defaults to enabling TLS for TCP routes and disabling unproxied ports for app containers. This has two primary benefits:

Traffic is encrypted between TCP Routers and applications, like how it is encrypted between Gorouter and applications.
Only the Gorouter and TCP Router can connect directly to app containers via the underlay network, which prevents unauthorized access to the applications.

Disabling TLS for TCP Routing

To disable TLS for TCP routing without causing TLS route downtime, you must follow a two-stage procedure:

Re-enable unproxied ports on all Diego cells by completing a BOSH deploy using the following ops files, as appropriate for your environment:
Disable TLS for TCP Routing by completing a second BOSH deploy adding the following ops files to the above ops files, as appropriate for your environment:

Configure TCP routing after deploying Cloud Foundry

After you activate TCP routing and deploy Cloud Foundry, you must add the TCP shared domain and configure org quotas that allow you to create TCP routes. To do this, you must use the Cloud Foundry Command Line Interface (cf CLI) and have an admin user account.

For more information about the cf CLI, see Using the Cloud Foundry Command Line Interface (cf CLI).

Configure Cloud Foundry with your TCP Domain

After you deploy Cloud Foundry, you must configure Cloud Foundry with the domain that you configured in Prerequisites for Enabling TCP Routing.

This is the domain from which developers create TCP routes.

To configure Cloud Foundry with your TCP domain:

To list your router groups, run:
```
cf router-groups
```
You must see default-tcp as a response.
Create a shared domain and associate it with the default-tcp router group by running:
```
cf create-shared-domain tcp.APP-DOMAIN.com --router-group default-tcp
```
Where APP-DOMAIN is the name of your app domain.
Verify that TCP appears under type next to your TCP domain by running:
```
cf domains
```

Configure a quota for TCP routes

Because TCP route ports are a limited resource in some environments, quotas are configured to allow creation of zero TCP routes by default. After you deploy Cloud Foundry, you can increase the maximum number of TCP routes for all orgs or for particular orgs and spaces. Because you reserve a route port for each TCP route, you manage the quota for route ports using the --reserved-route-ports cf CLI command option.

For more information, see Creating and Modifying Quota Plans.

You can configure quotas for TCP routes in the following ways:

If you have a default quota that applies to all orgs, you can update it to configure the number of route ports that can be reserved by each org by running:
```
cf update-org-quota QUOTA --reserved-route-ports NUMBER-OF-ROUTE-PORTS
```
Where:
- QUOTA is the maximum number of TCP routes you want to allocate to all orgs.
- NUMBER-OF-ROUTE-PORTS is the number of route ports you want to allow each org to reserve.
To create a new quota that governs the number of route ports that can be created in a particular org:
1. Target the org for which you want to create the quota by running:
```
cf target -o ORG-NAME
```
  Where ORG-NAME is the name of the org for which you want to create the quota.
2. Run:
```
create-org-quota QUOTA --reserved-route-ports NUMBER-OF-ROUTE-PORTS
```
  Where:
  - QUOTA is the maximum number of TCP routes you want to allocate to particular orgs.
  - NUMBER-OF-ROUTE-PORTS is the number of route ports you want to allow each org to reserve.
To create a new quota that governs the number of route ports that can be created in a particular space:
1. Target the space to create the quota by running:
```
cf target -s SPACE-NAME
```
  Where SPACE-NAME is the name of the space for which you want to create the quota.
2. Run:
```
cf create-space-quota QUOTA --reserved-route-ports NUMBER-OF-ROUTE-PORTS
```
  Where:
  - QUOTA is the maximum number of TCP routes you want to allocate to a particular space.
  - NUMBER-OF-ROUTE-PORTS is the number of route ports you want to allow the space to reserve.

Create a TCP route

For information about creating a TCP route, see Create a TCP Route with a Port in Configuring Routes and Domains.

Modify TCP port reservations

After deploying Cloud Foundry, you can modify the range of ports available for TCP routes using cf curl commands, as demonstrated with the following commands. The commands require you to have an admin user account with the routing.router_groups.read and routing.router_groups.write scopes.

In a terminal window, view the reservable_ports by running:
```
cf curl /routing/v1/router_groups
```
Record the guid from the output.
To configure a new port, run:
```
cf curl /routing/v1/router_groups/GUID
```
Where GUID is the GUID you recorded in the previous step.

To configure multiple ports, enter a comma-separated list of ports or port ranges by running:
```
cf curl \
-X PUT -d '{"reservable_ports":"PORTS-OR-PORT-RANGES"}' \
/routing/v1/router_groups/f7392031-a488-4890-8835-c4a038a3bded
```
Where PORTS-OR-PORT-RANGES is a comma-separated list of ports or port ranges. For example, "reservable_ports":"1024-1199,1234-1248,1312".

Important Do not enter reservable_ports that conflict with other TCP router instances or ephemeral port ranges. Cloud Foundry recommends using port ranges within 1024-2047 and 18000-32767 on default installations. Check which ports are available on the TCP router VMs to verify that no additional ports are in use. For more information, see TCP router fails to configure routes when there is a port conflict with a local process in the Routing Release repository on GitHub.

View the source for this page in GitHub