The example below focuses on hosting multiple [KeyDB](services/keydb.md) instances, but you can apply it to hosting multiple instances or whole stacks of any kind.
Let's say you're managing a host called `mash.example.com` which installs both [PeerTube](services/peertube.md) and [NetBox](services/netbox.md). Both of these services require a [KeyDB](services/keydb.md) instance. If you simply add `keydb_enabled: true` to your `mash.example.com` host's `vars.yml` file, you'd get a KeyDB instance (`mash-keydb`), but it's just one instance. As described in our [KeyDB](services/keydb.md) documentation, this is a security problem and potentially fragile as both services may try to read/write the same data and get in conflict with one another.
This creates a new group (called `mash_example_com`) which groups all 3 hosts:
- (**new**) `mash.example.com-netbox-deps` - a new host, for your [NetBox](services/netbox.md) dependencies
- (**new**) `mash.example.com-peertube-deps` - a new host, for your [PeerTube](services/peertube.md) dependencies
- (old) `mash.example.com` - your regular inventory host
When running Ansible commands later on, you can use the `-l` flag to limit which host to run them against. Here are a few examples:
-`just install-all` - runs the [installation](installing.md) process on all hosts (3 hosts in this case)
-`just install-all -l mash_example_com` - runs the installation process on all hosts in the `mash_example_com` group (same 3 hosts as `just install-all` in this case)
-`just install-all -l mash.example.com-netbox-deps` - runs the installation process on the `mash.example.com-netbox-deps` host
## Adjust the configuration of the supplementary hosts to use a new "namespace"
Multiple hosts targetting the same server as described above still causes conflicts, because services will use the same paths (e.g. `/mash/keydb`) and service/container names (`mash-keydb`) everywhere.
To avoid conflicts, adjust the `vars.yml` file for the new hosts (`mash.example.com-netbox-deps` and `mash.example.com-peertube-deps`)
and set non-default and unique values in the `mash_playbook_service_identifier_prefix` and `mash_playbook_service_base_directory_name_prefix` variables. Examples below:
Now that we've created separate KeyDB instances for both PeerTube and NetBox, we need to put them to use by editing the `vars.yml` file of the main host (the one that installs PeerTbue and NetBox) to wire them to their KeyDB instances.
**Can't I just create one host and a separate stack for each service** (e.g. Nextcloud + all dependencies on one inventory host; PeerTube + all dependencies on another inventory host; with both inventory hosts targetting the same server)?
> That's a possibility which is somewhat clean. The downside is that each "full stack" comes with its own Postgres database which needs to be maintained and upgraded separately.
