How to configure more complex networks using spaces

Juju provides a set of features allowing the users to have better and finer-grained control over the networking aspects of the environment and service deployments in particular. Not all cloud providers support these enhanced networking features yet, in fact they are currently supported on AWS only. Support for MAAS and OpenStack is planed and will be available in future releases of Juju.

Juju network spaces (or just "spaces") represent sets of disjoint subnets available for running cloud instances, which may span one or more availability zones ("zones"). Any given subnet can be part of one and only one space. All subnets within a space are considered "equal" in terms of access control, firewall rules, and routing. Communication between spaces on the other hand (e.g. between instances started in subnets part of different spaces) will be subject to access restrictions and isolation.

Having multiple subnets spanning different zones within the same space allows Juju to perform automatic distribution of units of a service across zones inside the same space. This allows for high-availability for services and spreading the instances evenly across subnets and zones.

As an example, consider an environment divided into three segments with distinct security requirements:

  • The "dmz" space for publicly-accessible services (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 "database" space for backend database services, 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 "database" space. All subnets within the "cms" and "database" spaces provide no access from outside the environment for security reasons. Using spaces for deployments like this allows Juju to have the necessary information about how to configure the firewall and access control rules. In this case, instances in "dmz" can only communicate with instances in "apps", which in turn are the only ones allowed to access instances in "database".

Please note, Juju does not yet enforce those security restrictions, but having spaces and subnets available makes it possible to implement those restrictions and access control in a future release.

Due to the ability of spaces to span multiple zones services can be distributed across these zones. This allows high available setup for services within the environment.

Spaces are created like this:

juju space create <name> [ <CIDR1> <CIDR2> ... ] [--private|--public]

They can be listed in various formats using the "list" subcommand. See also "juju space help" for more information. Other space subcommands are "list", "rename", and "remove".

Existing subnets can be added using:

juju subnet add <CIDR>|<subnet-provider-id> <space> [<zone1> <zone2> ...]

Like spaces they can be listed by the subcommand "list". See also "juju subnet help" for more information.

The commands "add-machine" and "deploy" allow the specification of a spaces constraint for the selection of a matching instance. It is done by adding:

--constraints spaces=<allowedspace1>,<allowedspace2>,^<disallowedspace>

The spaces constraint allows to select an instance for the new machine or unit, connected to one or more existing spaces. Both positive and negative entries are accepted, the latter prefixed by "^", in a comma-delimited list. For example, given the following:

--constraints spaces=db,^storage,^dmz,internal

Juju will provision instances connected to (with IP addresses on) one of the subnets of both db and internal spaces, and NOT connected to either the storage or dmz spaces.

For more information regarding constraints in general, see "juju help constraints".


Let's model the following deployment in Juju on AWS:

  • DMZ space (with 2 subnets, one in each zone), hosting 2 units of the haproxy service, which is exposed and provides access to the CMS application behind it.
  • CMS space (also with 2 subnets, one per zone), hosting 2 units of mediawiki, accessible only via haproxy (not exposed).
  • Database (again, 2 subnets, one per zone), hosting 2 units of mysql, providing the database backend for mediawiki.
  • We also assume the used AWS account has a default VPC for the chosen region (in the example we're using eu-central-1 region).

First, we need to create additional subnets within the default VPC, using the AWS Web Console, and enable the "automatic public IP address" attribute on each subnet:

  •, in zone "eu-central-1a" (for space "database")
  •, in zone "eu-central-1b" (for space "database")
  •, in zone "eu-central-1a" (for space "cms")
  •, in zone "eu-central-1b" (for space "cms")

We also assume the default VPC already has 2 default subnets (one per zone), configured like this:

  •, in zone "eu-central-1a" (we'll use it for the "dmz" space)
  •, in zone "eu-central-1b"(also for the "dmz" space)

Once the default VPC has those subnets, we can bootstrap as usual:

$ juju bootstrap

After that, we can create the 3 spaces and add the subnets we created to each one. These steps will be automated, and the subnet creation will be possible directly from Juju in a future release.

juju space create dmz
juju space create cms
juju space create database
juju subnet add dmz
juju subnet add dmz
juju subnet add database
juju subnet add database
juju subnet add cms
juju subnet add cms

Now we can deploy the services into their respective spaces, relate them and expose haproxy:

juju deploy haproxy -n 2 --constraints spaces=dmz
juju deploy mediawiki -n 2 --constraints spaces=cms
juju deploy mysql -n 2 --constraints spaces=database
juju add-relation haproxy mediawiki
juju add-relation mediawiki mysql
juju expose haproxy

Once all the units are up, you will be able to get the public IP address of one of the haproxy units (from juju status), and open it in a browser, seeing the mediawiki page.

In an upcoming release, Juju will provide much better visibility of which services and units run in which spaces/subnets.

Please note, Juju supports the described syntax but currently ignores all but the first allowed space in the list. This behavior will change in a future release. Also, only the EC2 provider supports spaces as described, with support for MaaS and OpenStack coming soon.

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