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📖 Fix comment on LeaderElectionResourceLock #1903

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May 25, 2022
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📖 Fix comment on LeaderElectionResourceLock #1903

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38 changes: 28 additions & 10 deletions pkg/manager/manager.go
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Original file line number Diff line number Diff line change
Expand Up @@ -142,18 +142,36 @@ type Options struct {
LeaderElection bool

// LeaderElectionResourceLock determines which resource lock to use for leader election,
// defaults to "configmapsleases". Change this value only if you know what you are doing.
// Otherwise, users of your controller might end up with multiple running instances that
// defaults to "leases". Change this value only if you know what you are doing.
//
// If you are using `configmaps`/`endpoints` resource lock and want to migrate to "leases",
// you might do so by migrating to the respective multilock first ("configmapsleases" or "endpointsleases"),
// which will acquire a leader lock on both resources.
// After all your users have migrated to the multilock, you can go ahead and migrate to "leases".
// Please also keep in mind, that users might skip versions of your controller.
//
// Note: before controller-runtime version v0.7, it was set to "configmaps".
// And from v0.7 to v0.11, the default was "configmapsleases", which was
// used to migrate from configmaps to leases.
// Since the default was "configmapsleases" for over a year, spanning five minor releases,
// any actively maintained operators are very likely to have a released version that uses
// "configmapsleases". Therefore defaulting to "leases" should be safe since v0.12.
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//
// So, what do you have to do when you are updating your controller-runtime dependency
// from a lower version to v0.12 or newer?
// - If your operator matches at least one of these conditions:
// - the LeaderElectionResourceLock in your operator has already been explicitly set to "leases"
// - the old controller-runtime version is between v0.7.0 and v0.11.x and the
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// LeaderElectionResourceLock wasn't set or was set to "leases"/"configmapsleases"/"endpointsleases"
// feel free to update controller-runtime to v0.12 or newer.
// - Otherwise, you may have to take these steps:
// 1. update controller-runtime to v0.12 or newer in your go.mod
// 2. set LeaderElectionResourceLock to "configmapsleases" (or "endpointsleases")
// 3. package your operator and upgrade it in all your clusters
// 4. only if you have finished 3, you can remove the LeaderElectionResourceLock to use the default "leases"
// Otherwise, your operator might end up with multiple running instances that
// each acquired leadership through different resource locks during upgrades and thus
// act on the same resources concurrently.
// If you want to migrate to the "leases" resource lock, you might do so by migrating to the
// respective multilock first ("configmapsleases" or "endpointsleases"), which will acquire a
// leader lock on both resources. After all your users have migrated to the multilock, you can
// go ahead and migrate to "leases". Please also keep in mind, that users might skip versions
// of your controller.
//
// Note: before controller-runtime version v0.7, the resource lock was set to "configmaps".
// Please keep this in mind, when planning a proper migration path for your controller.
LeaderElectionResourceLock string

// LeaderElectionNamespace determines the namespace in which the leader
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