Documentation
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Overview ¶
Package confsnap keeps a byte-for-byte copy of the host configuration files that more than one node stack writes, so a failed migration or upgrade can put them back. A snapshot is a directory: a blob per regular file and a manifest that records every path, its kind, mode and owner. The manifest is written last and atomically, so a snapshot that exists is complete and a crash while taking one leaves nothing to restore.
Snapshots hold credentials (kubelet client keys), so the directory and the blobs are private to the owner.
Index ¶
Constants ¶
This section is empty.
Variables ¶
var ErrNoSnapshot = errors.New("no configuration snapshot")
ErrNoSnapshot is returned by Restore when dir holds no complete snapshot.
var ErrSnapshotExists = errors.New("a configuration snapshot already exists")
ErrSnapshotExists is returned by Take when dir already holds a complete snapshot. That snapshot is the only record of a configuration a crash may have interrupted the restore of, so it is never overwritten: the caller restores or discards it first.
Functions ¶
func PathsFor ¶
PathsFor returns SharedPaths plus the host paths that the node stacks of the given modes write in place, so a snapshot taken before one of them is built restores everything it can overwrite. A container slot's rootfs maps the same-path directories to the host, so preparing one writes the host's CNI plugins (/opt/cni/bin) while the old slot still runs.
func Restore ¶
Restore puts every recorded path back as it was when the snapshot was taken: the same bytes, mode, owner and links. Files that were created below a recorded directory since are removed, and a path recorded as absent is removed. It is idempotent, and leaves a file alone when it already matches. Every path is attempted, and the errors are joined.
func SharedPaths ¶
func SharedPaths() []string
SharedPaths returns the host configuration paths that the node stacks of different isolation modes (or two versions of one) both write, at the same location: the containerd and kubelet configuration, the kubelet identity and PKI, the CNI configuration and the LocalDNS files. Units and binaries are not here; each backend restores those itself. The list is a superset: a path a mode does not use on the host is recorded as absent and stays absent.
func Take ¶
Take records the state of paths, which are absolute in-node paths, below root (empty means the real filesystem root) into dir. A complete snapshot already in dir is refused with ErrSnapshotExists; an incomplete one, which a crash during an earlier Take leaves, is replaced. The snapshot is durable once Take returns: every saved file and the manifest are synced, the manifest last, so a manifest on disk always names files that are there. A directory is recorded with everything below it; symbolic links are recorded, not followed. A path that does not exist is recorded as absent. Sockets, devices and other special files are an error, since they cannot be put back.
Source Files