autoupdate: implement time-based strategy

This commit implements the time-based rollout strategy describen in
RFD 184. The autoupdate_agent_rollout controller will make the groups
active based on their start days, start hour, and maintenance duration.
Once the maintenance window is over, the group becomes DONE.
In the DONE state, new agents will instalkl the target version but
existing agents will no longer be told to actively update.

lib/autoupdate/rollout/strategy_timebased.go

@@ -0,0 +1,110 @@
+/*
+ * Teleport
+ * Copyright (C) 2024  Gravitational, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package rollout
+
+import (
+	"context"
+	"log/slog"
+
+	"github.com/gravitational/trace"
+	"github.com/jonboulle/clockwork"
+
+	"github.com/gravitational/teleport/api/gen/proto/go/teleport/autoupdate/v1"
+	update "github.com/gravitational/teleport/api/types/autoupdate"
+)
+
+const (
+	updateReasonInWindow      = "in_window"
+	updateReasonOutsideWindow = "outside_window"
+)
+
+type timeBasedStrategy struct {
+	log   *slog.Logger
+	clock clockwork.Clock
+}
+
+func (h *timeBasedStrategy) name() string {
+	return update.AgentsStrategyTimeBased
+}
+
+func newTimeBasedStrategy(log *slog.Logger, clock clockwork.Clock) (rolloutStrategy, error) {
+	if log == nil {
+		return nil, trace.BadParameter("missing log")
+	}
+	if clock == nil {
+		return nil, trace.BadParameter("missing clock")
+	}
+	return &timeBasedStrategy{
+		log:   log.With("strategy", update.AgentsStrategyTimeBased),
+		clock: clock,
+	}, nil
+}
+
+func (h *timeBasedStrategy) progressRollout(ctx context.Context, groups []*autoupdate.AutoUpdateAgentRolloutStatusGroup) error {
+	now := h.clock.Now()
+	// We always process every group regardless of the order.
+	var errs []error
+	for _, group := range groups {
+		switch group.State {
+		case autoupdate.AutoUpdateAgentGroupState_AUTO_UPDATE_AGENT_GROUP_STATE_UNSTARTED,
+			autoupdate.AutoUpdateAgentGroupState_AUTO_UPDATE_AGENT_GROUP_STATE_DONE:
+			// We start any group unstarted group in window.
+			// Done groups can transition back to active if they enter their maintenance window again.
+			// Some agents might have missed the previous windows and might expected to try again.
+			shouldBeActive, err := inWindow(group, now)
+			if err != nil {
+				// In time-based rollouts, groups are not dependent.
+				// Failing to transition a group should affect other groups.
+				// We reflect that something went wrong in the status and go to the next group.
+				setGroupState(group, group.State, updateReasonReconcilerError, now)
+				errs = append(errs, err)
+				continue
+			}
+			if shouldBeActive {
+				setGroupState(group, autoupdate.AutoUpdateAgentGroupState_AUTO_UPDATE_AGENT_GROUP_STATE_ACTIVE, updateReasonInWindow, now)
+			} else {
+				setGroupState(group, group.State, updateReasonOutsideWindow, now)
+			}
+		case autoupdate.AutoUpdateAgentGroupState_AUTO_UPDATE_AGENT_GROUP_STATE_ROLLEDBACK:
+			// We don't touch any group that was manually rolled back.
+			// Something happened and we should not try to update again.
+		case autoupdate.AutoUpdateAgentGroupState_AUTO_UPDATE_AGENT_GROUP_STATE_ACTIVE:
+			// The group is currently being updated. We check if the maintenance
+			// is over and if we should transition it to the done state
+			shouldBeActive, err := inWindow(group, now)
+			if err != nil {
+				// In time-based rollouts, groups are not dependent.
+				// Failing to transition a group should affect other groups.
+				// We reflect that something went wrong in the status and go to the next group.
+				setGroupState(group, group.State, updateReasonReconcilerError, now)
+				errs = append(errs, err)
+				continue
+			}
+
+			if shouldBeActive {
+				setGroupState(group, autoupdate.AutoUpdateAgentGroupState_AUTO_UPDATE_AGENT_GROUP_STATE_ACTIVE, updateReasonInWindow, now)
+			} else {
+				setGroupState(group, autoupdate.AutoUpdateAgentGroupState_AUTO_UPDATE_AGENT_GROUP_STATE_DONE, updateReasonOutsideWindow, now)
+			}
+		default:
+			return trace.BadParameter("unknown autoupdate group state: %v", group.State)
+		}
+	}
+	return trace.NewAggregate(errs...)
+}