mv index allocate to shard allocate, add explanations, fixes #71 (#75)

pkg/es/shard.go

@@ -145,3 +145,63 @@ func ShardShow(conf *cfg.Config, index string) error {
 
 	return printShards(conf, res)
 }
+
+func ShardAllocation(conf *cfg.Config, index string) error {
+	explain := conf.DefaultCluster.ES().Cluster.AllocationExplain().
+		Index(index).
+		Primary(conf.Primary).
+		Shard(conf.Shards)
+
+	if conf.FromNode != "" {
+		explain.CurrentNode(conf.FromNode)
+	}
+
+	res, err := explain.Do(context.Background())
+	if err != nil {
+		return fmt.Errorf("failed to get shard allocation explain: %s", esErrorString(err))
+	}
+
+	slog.Debug("ES result", "explain", res)
+
+	currentNode := res.CurrentNode
+
+	table := printer.NewTable(conf, 2, 10)
+	table.Addheaders("shard allocation setting", "value")
+
+	roles := make([]string, len(currentNode.Roles))
+	for idx, role := range currentNode.Roles {
+		roles[idx] = role.Name
+	}
+
+	table.Entries = [][]any{
+		{"Index", index},
+		{"Current state", res.CurrentState},
+		{"Current node", currentNode.Name},
+		{"Current k8s node", currentNode.Attributes["k8s_node_name"]},
+		{"Current node address", currentNode.TransportAddress},
+		{"Current node id", currentNode.Id},
+		{"Current node weight", currentNode.WeightRanking},
+		{"Current node roles", roles},
+		{"Can rebalance cluster", res.CanRebalanceCluster.Name},
+		{"Can rebalance to another node", res.CanRebalanceToOtherNode.Name},
+		{"Can remain on current node", res.CanRemainOnCurrentNode.Name},
+	}
+
+	if res.CurrentState == "unassigned" {
+		table.AddRow("Unassignment reason", res.UnassignedInfo.Reason.String()+" at "+res.UnassignedInfo.At.(string))
+	}
+
+	for _, nodeDecision := range res.NodeAllocationDecisions {
+		for _, decider := range nodeDecision.Deciders {
+			table.AddRow("Allocation decider", decider.Decider)
+			table.AddRow("    -> decision", decider.Decision.String())
+			table.AddRow("    -> explanation", decider.Explanation)
+		}
+	}
+
+	if err := table.Print(); err != nil {
+		return err
+	}
+
+	return nil
+}