66cc593886
Since instances that have ephemeral volumes, which we plan to use for persistent state (yes the name is confusing) start with the volume empty, we need some support to aid in placing state files (and configuration files we want to generate dynamically) on that partition - we can't just move stuff there during build, or it will be mounted over by cloud-init. Change-Id: Iff9e329ba6217e5f7290b7ab65b1808f4a8d8f9a
2.1 KiB
Provides tools to aid in relocating state to /mnt/state
In a cloud instance /mnt/state is on the cloud ephemeral device when one exists, or the root when one doesn't.
The pattern for having state on /mnt/state is:
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The service/daemon can make its own state files on startup (as /mnt is always empty on first-boot).
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Alternatively os-refresh-config can be used to populate any initial state so that the daemon/service works (so until the first os-refresh-config run that daemon/service will be broken).
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If the state needs migrating (e.g. PostgreSQL 9.1 to 9.2) then a migration script should be added to os-refresh-config's migrations.d tree to perform that migration that state (if the migration can be done after the service starts) or to configure.d if the service cannot start without the migration being done).
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state should live in /mnt/state/original-path e.g. /mnt/state/etc/ssh/ssh_host_dsa_key.
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where there are hardcoded specific paths, we leave symlinks in that path pointing into /mnt/state - e.g. /etc/ssh/ss_host_dsa_key will be a symlink to /mnt/state/etc/ssh/ssh_host_dsa_key.
To factor out common code elements can invoke register-state-path during install.d to request that a particular path be registered as a stateful path.
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If there is content at the path at registration time, it will be moved to /var/lib/use-ephemeral/original-path.
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If --leave-symlink is passed, a symlink will be created at that path pointing to /mnt/state/original-path.
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Stateful paths are listed in /var/lib/use-ephemeral/stateful-paths, one path per line - e.g. /etc/ssh/ssh_host_dsa_key.
Once registered:
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During pre-configure.d the parent directories leading up to the path will be asserted on startup.
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If there is a content at /var/lib/use-ephemeral/original-path during pre-configure.d, and the new path does not exist in /mnt/state then an rsync -a will be made into /mnt/state/original-path reinstating a pristine copy of what was preserved. This is only done when the path does not exist to avoid corrupting evolved or migrated state.