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Guidelines for safely updating an AppArmor system

AppArmor is a system of interconnected components that can break in some situations if changes are not applied in the correct order.

When ordering is important

Minor updates of any component of AppArmor should not result in breakage, and those changes should be safe to roll out in any order that is convenient. For example adding new rules to a policy file, bug fixes to the compiler, or kernel, should all be safe to roll out without any concerns to ordering.

When a new feature or semantic change is introduced ordering of role out is important.

Preparing for changes

Significant changes should be staged and well tested before being checked in. Testing needs to include component compatibility testing. That is new parser on old kernel, and new kernel on old parser, if either of these have changes.

Check in of changes should occur in the same order as recommended rollout, to guarentee that the archive is in a consistent working state for any given snapshot.

Order of roll out

The kernel and parser should be introduced first. The ordering of these should not generally matter, as long as the kernel keeps it interface stable. If there is any doubt the parser should be rolled out first as it is required to work with older and newer interfaces, because in live update install situations, the new kernel will not be live until a reboot.

After the parser and kernel are updated, the surrounding tools should be updated.

The policy is the last component that should be updated. As it may contain rules expressing new features that require and updated parser and kernel.