plugin/nomad: Add a Nomad plugin (#7467)

Signed-off-by: Olli Janatuinen <olli.janatuinen@gmail.com>

plugin/nomad/setup.go

@@ -0,0 +1,141 @@
+package nomad
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/coredns/caddy"
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+
+	nomad "github.com/hashicorp/nomad/api"
+)
+
+// init registers this plugin.
+func init() { plugin.Register(pluginName, setup) }
+
+// setup is the function that gets called when the config parser sees the token "nomad". Setup is responsible
+// for parsing any extra options the nomad plugin may have. The first token this function sees is "nomad".
+func setup(c *caddy.Controller) error {
+	n := &Nomad{
+		ttl:     uint32(defaultTTL),
+		clients: make([]*nomad.Client, 0),
+		current: -1,
+	}
+
+	// Parse the configuration, including the zone argument
+	if err := parse(c, n); err != nil {
+		return plugin.Error("nomad", err)
+	}
+
+	c.OnStartup(func() error {
+		var err error
+		for idx, client := range n.clients {
+			_, err := client.Agent().Self()
+			if err == nil {
+				n.current = idx
+				return nil
+			}
+		}
+		return err
+	})
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		n.Next = next
+		return n
+	})
+
+	return nil
+}
+
+func parse(c *caddy.Controller, n *Nomad) error {
+	var token string
+	addresses := []string{} // Multiple addresses are stored here
+
+	// Expect the first token to be "nomad"
+	if !c.Next() {
+		return c.Err("expected 'nomad' token")
+	}
+
+	// Check for the zone argument
+	args := c.RemainingArgs()
+	if len(args) == 0 {
+		n.Zone = "service.nomad"
+	} else {
+		n.Zone = args[0]
+	}
+
+	// Parse the configuration block
+	for c.NextBlock() {
+		selector := strings.ToLower(c.Val())
+
+		switch selector {
+		case "address":
+			args := c.RemainingArgs()
+			if len(args) == 0 {
+				return c.Err("at least one address is required")
+			}
+			addresses = append(addresses, args...)
+		case "token":
+			args := c.RemainingArgs()
+			if len(args) != 1 {
+				return c.Err("exactly one token is required")
+			}
+			token = args[0]
+		case "ttl":
+			args := c.RemainingArgs()
+			if len(args) != 1 {
+				return c.Err("exactly one ttl value is required")
+			}
+			t, err := strconv.Atoi(args[0])
+			if err != nil {
+				return c.Err("error parsing ttl: " + err.Error())
+			}
+			if t < 0 || t > 3600 {
+				return c.Errf("ttl must be in range [0, 3600]: %d", t)
+			}
+			n.ttl = uint32(t)
+		default:
+			return c.Errf("unknown property '%s'", selector)
+		}
+	}
+
+	// Push an empty address to create a client solely based on the defaults.
+	if len(addresses) == 0 {
+		addresses = append(addresses, "")
+	}
+
+	for _, addr := range addresses {
+		cfg := nomad.DefaultConfig()
+		if len(addr) > 0 {
+			cfg.Address = addr
+		}
+		if len(token) > 0 {
+			cfg.SecretID = token
+		}
+		client, err := nomad.NewClient(cfg)
+		if err != nil {
+			return plugin.Error("nomad", err)
+		}
+		n.clients = append(n.clients, client) // Store all clients
+	}
+
+	return nil
+}
+
+func (n *Nomad) getClient() (*nomad.Client, error) {
+	// Don't bother querying Agent().Self() if there is only one client.
+	if len(n.clients) == 1 {
+		return n.clients[0], nil
+	}
+	for i := range len(n.clients) {
+		idx := (n.current + i) % len(n.clients)
+		_, err := n.clients[idx].Agent().Self()
+		if err == nil {
+			n.current = idx
+			return n.clients[idx], nil
+		}
+	}
+	return nil, fmt.Errorf("no Nomad client available")
+}