Constellation gives you the capability to create UNIX users which can connect to the cluster nodes over SSH, allowing you to access both control-plane and worker nodes. While the nodes' data partitions are persistent, the system partitions are read-only. Consequently, users need to be re-created upon each restart of a node. This is where the Access Manager comes into effect, ensuring the automatic (re-)creation of all users whenever a node is restarted.
During the initial creation of the cluster, all users defined in the `ssh-users` section of the Constellation configuration file are automatically created during the initialization process. For persistence, the users are stored in a ConfigMap called `ssh-users`, residing in the `kube-system` namespace. For a running cluster, users can be added and removed by modifying the entries of the ConfigMap and performing a restart of a node.
The Access Manager is deployed as a DaemonSet called `constellation-access-manager`, running as an `initContainer` and afterward running a `pause` container to avoid automatic restarts. While technically killing the Pod and letting it restart works for the (re-)creation of users, it doesn't automatically remove users. Thus, a complete node restart is required after making changes to the ConfigMap.
When a user is deleted from the ConfigMap, it won't be re-created after the next restart of a node. The home directories of the affected users will be moved to `/var/evicted`, with the owner of each directory and its content being modified to `root`.
You can update the ConfigMap by:
```bash
kubectl edit configmap -n kube-system ssh-users
```
Or alternatively, by modifying and re-applying it with the definition listed in the examples.
## Examples
An example to create an user called `myuser` as part of the `constellation-config.yaml` looks like this:
```yaml
# Create SSH users on Constellation nodes upon the first initialization of the cluster.
sshUsers:
myuser: "ssh-rsa AAAA...mgNJd9jc="
```
This user is then created upon the first initialization of the cluster, and translated into a ConfigMap as shown below:
```yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: ssh-users
namespace: kube-system
data:
myuser: "ssh-rsa AAAA...mgNJd9jc="
```
Entries can be added simply by adding `data` entries:
```yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: ssh-users
namespace: kube-system
data:
myuser: "ssh-rsa AAAA...mgNJd9jc="
anotheruser: "ssh-ed25519 AAAA...CldH"
```
Similarly, removing any entries causes users to be evicted upon the next restart of the node.
