Network Spaces

Juju models networks using spaces, which can be mapped to one or more subnets of the chosen backing cloud. When a space's subnets span multiple availability zones Juju will automatically distribute application units across subnets and zones, thereby providing a degree of high-availability.

From a security standpoint, with spaces, the Juju environment network topology can be organised in a way such that applications possess only the network connectivity they require.

Here are a few properties to keep in mind:

• Any given subnet can be part of one and only one space.
• All subnets within a space are considered "equal" in terms of routing.

Use case

Consider a model divided into three segments with distinct security requirements:

• The "dmz" space for publicly-accessible applications (e.g. HAProxy) providing access to the CMS application behind it.
• The "cms" space for content-management applications accessible via the "dmz" space only.
• The "db" space for backend database applications, which should be accessible only by the applications.

HAProxy is deployed inside the "dmz" space, it is accessible from the internet and proxies HTTP requests to one or more Joomla units in the "cms" space. The backend MySQL for Joomla is running in the "db" space. All subnets within the "cms" and "db" spaces provide no access from outside the environment for security reasons.

Adding and listing spaces and subnets

Spaces are created with the add-space command. The following command maps a space called db-space with subnet 192.168.123.0/24:

juju add-space db-space 192.168.123.0/24

To see which spaces have been added, along with any subnets belonging to those spaces, use the juju spaces command. Its output will look similar to the following:

Space    Subnets
db-space 192.168.123.0/24
public
undefined  192.168.122.0/24

To map an existing subnet to a space use the add-subnet command. Here we map subnet 192.168.124.0/24 to space 'db-space':

juju add-subnet 192.168.124.0/24 db-space

The juju subnets command will list all subnets known to Juju with output similar to the following:

subnets:
  192.168.122.0/24:
    type: ipv4
    provider-id: "5"
    status: in-use
    space: undefined
    zones:
    - default
  192.168.123.0/24:
    type: ipv4
    provider-id: "6"
    status: in-use
    space: undefined
    zones:
    - default

MAAS and spaces

MAAS has a native knowledge of spaces. Within MAAS, spaces can be created, configured, and destroyed. This allows Juju to leverage MAAS spaces without the need to add/remove spaces and subnets. However, this also means that Juju needs to "pull" such information from MAAS. This is done by default upon controller-creation. Run juju reload-spaces to refresh Juju's knowledge of MAAS spaces and works on a per-model basis.

Bridges

Juju creates bridges for containers only when Juju knows the spaces an application may require, and the container's bridge for that application will only connect to the required network interfaces.

Using spaces

Once all desired spaces have been added and/or configured they can be called upon using either a constraint or a binding:

• A space constraint, like any other constraint, operates at the machine level. It requests that certain network connections be made available to the Juju machine. When a constraint is used, all application endpoints get associated with the space.

  • See the Using constraints page to learn more about constraints.
  • For examples of using the 'spaces' constraint, read Deploying to spaces for how to use it with the deploy command and Setting constraints when adding a machine for how to use it with the add-machine command.

• A binding is a space-specific, software level operation and is a more fine-grained request. It associates an application endpoint with a subnet.

  See examples of using a binding when deploying applications on Deploying to network spaces. For using spaces with bundles go to Charm bundles.