RedHat systemd configuration

Instructions for enabling systemd units on RHEL-based and compatible systems.

As of DSE version 6.0.13, systemd units are now included for RHEL-based and compatible systems.

The following units are installed in /usr/lib/systemd/system:

dse.target: starts DSE nodes
dse-shutdown.target: stops DSE nodes

In addition, a dse@.service template is installed into /usr/share/dse/templates and serves as a template unit for all DSE node instances running on the host OS under the cassandra user. That template is used by the dse add-node command and the /usr/share/dse/tools/dse-convert-to-systemd helper script.

Once dse.target is enabled, the dse add-node command creates and enables systemd service for new nodes, and also creates init.d scripts to redirect lifecycle commands to systemctl.

By default, systemd units are not enabled. Old init.d scripts remain in effect.

Tip: On systems that have systemd, the old init.d services can still be manipulated usiing systemd commands, for instance,

systemctl start
                        dse

To enable DSE systemd units:

Stop the DSE init.d service:
```
sudo service dse stop
```
Enable dse.target:
```
sudo systemctl enable dse.target
```
Note: After dse.target is enabled, DSE nodes automatically start as part of the multi-user target on each reboot.
On each node run:
```
sudo /usr/share/dse/tools/dse-convert-to-systemd full-node-id
```
Note: The node address, full-node-id must be the full node ID including the dse- prefix. The default node ID if no other nodes are configured is dse.
```
/usr/share/dse/tools/dse-convert-to-systemd dse-node1
```
The dse-convert-tosystemd script makes the following changes:
- Creates and enables systemd units for DSE nodes in /etc/systemd/system/.
- Modifies the DSE init.d script to redirect lifecycle commands to systemctl.

What's next

DSE systemd operations include:

Start all DSE nodes:
```
systemctl start dse.target
```
Stop all DSE nodes:
```
systemctl start dse-shutdown.target
```
Start one DSE node:
```
systemctl start full-node-id
```
Stop one DSE node:
```
systemctl stop full-node-id
```

Note: The node address, full-node-id must be the full node ID including the dse- prefix. The default node ID if no other nodes are configured is dse.

Tip: The default start timeout is 10 minutes and the default stop timeout is 30 seconds. Those values can be adjusted by editing the corresponding unit files.