The container-to-container networking feature allows direct network traffic between apps. For an overview of how Container-to-Container Networking works, see Container-to-Container Networking. Note that Container-to-container networking is not available for apps hosted on Windows.

Container-to-container networking enables VMware Tanzu Application Service for VMs (TAS for VMs) to generate logs whenever containers communicate or attempt to communicate with each other. For more information about managing app traffic logging, see the App Traffic Logging section of the Configuring Logging in TAS for VMs topic.

Configure the Overlay Network

Container-to-container networking uses an overlay network to manage communication between app instances. By default, each Diego Cell in the overlay network is allocated a /24 range that supports 254 containers per Diego Cell, one container for each of the usable IP addresses, .1 through .254. For more information about the overlay network, see Overlay network in Container-to-Container Networking.

Configure the Number of Diego Cells

To modify the number of Diego Cells supported by the overlay network:

  1. In Ops Manager, click the TAS for VMs tile.

  2. Click Networking.

  3. Under Overlay Subnet, enter an IP range for the overlay network. By default, Ops Manager uses 10.255.0.0/16. Modifying the subnet range allocated to the overlay network changes the number of Diego Cells supported in your deployment. Use the table below as a reference.

Overlay subnet mask Number of Diego Cells Containers per Diego Cell
/20 15 254
/16 255 254
/12 4,095 254

The overlay network IP address range must not conflict with any other IP addresses in the network. If a conflict exists, Diego Cells cannot reach any endpoint that has a conflicting IP address.

Create and manage networking policies

This section describes how to create and modify Container-to-Container Networking policies using the Cloud Foundry Command Line Interface (cf CLI).

Note: You can also create and modify container-to-container networking policies using Apps Manager. For more information, see Create Container-to-Container Networking Policies in the Managing Apps and Service Instances Using Apps Manager topic.

Prerequisites

Ensure that you are using cf CLI v6.42 or later:

$ cf version

For more information about updating the cf CLI, see the Installing the cf CLI topic.

Grant permissions

CF admins use the following UAA scopes to grant specific users or groups permissions to configure network policies:

UAA Scope Suitable for… Allows users to create policies…
network.admin operators for any apps in the CF deployment
network.write space developers for apps in spaces that they can access

If you are a CF admin, you already have the network.admin scope. An admin can also grant the network.admin scope to a space developer.

For more information, see Creating and Managing Users with the UAA CLI (UAAC) and Orgs, Spaces, Roles, and Permissions.

To grant all Space Developers permissions to configure network policies, open the App Developer Controls pane in the TAS for VMs tile and enable the Allow space developers to manage network policies check box.

Add a network policy

To add a policy that allows direct network traffic from one app to another, run the following command:

cf add-network-policy SOURCE_APP DESTINATION_APP -s DESTINATION_SPACE_NAME -o DESTINATION_ORG_NAME --protocol (tcp | udp) --port RANGE

Replace the placeholders in the above command as follows:

  • SOURCE_APP is the name of the app that sends traffic.
  • DESTINATION_APP is the name of the app that will receive traffic.
  • DESTINATION_SPACE_NAME is the space of the destination app. The default is the targeted space.
  • DESTINATION_ORG_NAME is the org of the destination app. The default is the targeted org.
  • PROTOCOL is one of the following: tcp or udp.
  • RANGE are the ports at which to connect to the destination app. The allowed range is from 1 to 65535. You can specify a single port, such as 8080, or a range of ports, such as 8080-8090.

The following example command allows access from the frontend app to the backend app over TCP at port 8080:

$ cf add-network-policy frontend backend --protocol tcp --port 8080
Adding network policy to app frontend in org my-org / space dev as admin...
OK

Space Developers can add up to 150 network policies per space. This limit does not apply to users with the network.admin scope.

List policies

You can list all the policies in your space, or just the policies for which a single app is the source:

  • To list the all the policies in your space, run cf network-policies.

    $ cf network-policies

  • To list the policies for an app, run cf network-policies --source MY-APP. Replace MY-APP with the name of your app.

    $ cf network-policies --source example-app

    The following example command lists policies for the app frontend:

    $ cf network-policies --source frontend
Listing network policies in org my-org / space dev as admin...

source      destination   protocol   ports    destination space    destination org
frontend    backend       tcp        8080     example-space        example-org

Remove a network policy

To remove a policy that allows direct network traffic from an app, run the following command:

cf remove-network-policy SOURCE_APP DESTINATION_APP -s DESTINATION_SPACE_NAME -o DESTINATION_ORG_NAME --protocol PROTOCOL --port RANGE

Replace the placeholders in the above command to match an existing policy, as follows:

  • SOURCE_APP is the name of the app that sends traffic.
  • DESTINATION_APP is the name of the app that receives traffic.
  • DESTINATION_SPACE_NAME is the space of the destination app. The default is the targeted space.
  • DESTINATION_ORG_NAME is the org of the destination app. The default is the targeted org.
  • PROTOCOL is either tcp or udp.
  • PORTS are the ports connecting the apps. The allowed range is from 1 to 65535. You can specify a single port, such as 8080, or a range of ports, such as 8080-8090.

The following command deletes the policy that allowed the frontend app to communicate with the backend app over TCP on port 8080:

$ cf remove-network-policy frontend backend --protocol tcp --port 8080
Removing network policy to app frontend in org my-org / space dev as admin...
OK

Disable network policy enforcement

You can disable Silk network policy enforcement between apps. Disabling network policy enforcement allows all apps to send network traffic to all other apps in the foundation despite no policy specifically allowing it.

To disable network policy enforcement between apps, do the following:

  1. Go to Ops Manager Installation Dashboard.

  2. Deactivate the Enable Silk Network Policy Enforcement check box.

  3. Click Save.

App service discovery

With app service discovery, apps pushed to TAS for VMs can establish container-to-container communications through a known route served by internal BOSH DNS. This allows front end apps to easily connect with back end apps.

Note: The internal domain used for service discovery is apps.internal by default. Operators can modify this value in App Developer Controls pane of the TAS for VMs tile.

To establish container-to-container communications between a front end and back end app, a developer:

  1. Launches a back end app that publishes a local endpoint.
  2. Maps a named route to the endpoint.
  3. Creates a network policy that allows direct traffic from the front end to the back end app.
  4. Launches the front end app.

See Cats and Dogs with Service Discovery in GitHub for an example, written in Go, that demonstrates communication between front end and back end apps.

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