Separate logs from /var on Fuel Master

Create separate partition for /var/log in order to isolate logs from other data on the Fuel Master to avoid service interruptions.

Problem description

Many services can be disrupted if /var partition fills up. A list of issues includes:

  • Corruption of postgres DB
  • Corruption of ext4 filesystem inside Docker container
  • Read-only mount of Docker containers
  • Corruption of SQLite DB of docker
  • Corruption of devicemapper metadata used by Docker
  • Diagnostic snapshot fails to write
  • pidfiles for services cannot be written

Solving each of these issues is possible and documented, but the root cause is unchecked growth of logs data filling up the /var partition.

Proposed change

Create new partition for /var/log during Fuel Master installation. The intended result is the following breakdown of disk space: * 10GB root filesystem (/) (unchanged) * 2-4gb swap (unchanged) * Greater of 5gb or 30% of remaining disk space for /var * Greater of 5gb or 40% of remaining disk space for /var/log * 1GB for Docker metadata* * Greater of 8gb or 30% of remaining disk space for Docker main data*

(* Docker changes tracked in

This change will not be made available to existing installations and will not be applied during Fuel Master upgrade.


There may be other ways to impose quotas on rsyslog and logrotate, but it generally runs as root user, both of which cannot be restricted. The other option is to simply avoid creating a new partition for /var/log. It would be possible to move just Docker data out of /var, but the Docker SQLite DB is still vulnerable in this case.

Data model impact


REST API impact


Upgrade impact

This feature is not possible to automatically implement during upgrades because it is not possible to reduce the size of the XFS partition of /var for versions of Fuel below 6.1. This is an XFS limitation. The only workaround is to copy the data to an external disk, recreate the logvol and filesystem. This process is delicate and could be documented, but not automated safely.

That having been said, docker daemon args will vary between new installations and upgraded installations. There is already a distinction in fuel-library for the host Puppet manifests which provides this.

Security impact


Notifications impact


Other end user impact


Performance Impact


Other deployer impact


Developer impact




Primary assignee:
Matthew Mosesohn <>
Other contributors:

Work Items

  • Create new /var/log logvol in installation


The test can be confirmed by creating a large file in /var/log and ensuring that no services are interrupted. Such a test would include deploying a new OpenStack environment.

Beyond a simple check here, the existing test suites in place are adequate to validate this spec.

Documentation Impact

A manual conversion document will be added to the Operations Guide for Fuel in order to allow those who wish to manually adjust their systems to take advantage of this feature.