a9s Parachute

This section describes the operation of a9s Parachute component.

The a9s Parachute is intended to ensure that certain services are stopped properly in the event of a disk filling up, in order to prevent data loss. For this purpose, the a9s Parachute runs on every a9s Data Service Instance. The a9s Parachute monitors both the ephemeral and the persistent disk and as soon as the disk usage exceeds a configured threshold, the a9s Parachute stops the configured services.

Configuration

The a9s Parachute can be configured via the following BOSH properties:

Property	Default Value	Description
a9s-parachute.ephemeral.usage_limit	80	Limit in percent for the ephemeral disk usage. 0 deactivates the check.
a9s-parachute.persistent.usage_limit	80	Limit in percent for the persistent disk usage. 0 deactivates the check.
a9s-parachute.services_to_stop		An array with the names of the monit processes to stop when the usage limit for a disk is reached. If no process names are specified, an error is raised.

Observability

To make the a9s Parachute observable, the following lock files are created in the /var/vcap/sys/run/a9s-parachute directory on the VM of the respective node of the service instance when the a9s Parachute is triggered:

• a9s-parachute-activated: Indicates that the a9s Parachute has been triggered and the configured services have been stopped
• a9s-parachute-activated-ephemeral: Indicates that the a9s Parachute for the ephemeral disk has been triggered
• a9s-parachute-activated-persistent: Indicates that the a9s Parachute for the persistent disk has been triggered

Keep in mind, if the a9s Parachute wasn't triggered the above file will not exist and the directory /var/vcap/sys/run/a9s-parachute will be empty.

Manually Restart a Service Instance’s Node

To manually restart the processes of a service instance's node and re-enable the a9s Parachute so that it stops the configured processes again when a disk fills up, the following steps are necessary:

1. SSH into the affected node of the service instance via `bosh -d <deployment_name> ssh <instance_name>
2. Become root via sudo -i
3. Remove all a9 Parachute lock files via rm -rf /var/vcap/sys/run/a9s-parachute
4. Enable the a9s Parachute checks via monit start ephemeral and monit start persistent
5. Start the stopped processes via monit start <process_name>

Keep in mind that the a9s Parachute doesn't clear up disk space, so you have to free up the disk space manually.

Resource Considerations

For more information, see a9s Parachute Resources Considerations.