From d66fd98d4a8f43b290d19ba7e46cf2d1f669db82 Mon Sep 17 00:00:00 2001
From: Nick Cabatoff <ncabatoff@hashicorp.com>
Date: Thu, 21 Oct 2021 10:10:48 -0400
Subject: [PATCH] Add support for go-sockaddr templated addresses in config.
 (#9109)

---
 changelog/9109.txt                            |  3 ++
 command/server/config.go                      | 11 ++++++
 command/server/config_test.go                 |  4 ++
 command/server/config_test_helpers.go         | 37 +++++++++++++++++++
 internalshared/configutil/listener.go         | 30 +++++++++++++++
 .../docs/configuration/listener/tcp.mdx       |  8 +++-
 6 files changed, 91 insertions(+), 2 deletions(-)
 create mode 100644 changelog/9109.txt

diff --git a/changelog/9109.txt b/changelog/9109.txt
new file mode 100644
index 000000000..c85db60b0
--- /dev/null
+++ b/changelog/9109.txt
@@ -0,0 +1,3 @@
+```release-note:improvement
+core: Add support for go-sockaddr templated addresses in config.
+```
diff --git a/command/server/config.go b/command/server/config.go
index df6938755..c478906a7 100644
--- a/command/server/config.go
+++ b/command/server/config.go
@@ -392,6 +392,17 @@ func ParseConfig(d, source string) (*Config, error) {
 		return nil, err
 	}
 
+	if rendered, err := configutil.ParseSingleIPTemplate(result.APIAddr); err != nil {
+		return nil, err
+	} else {
+		result.APIAddr = rendered
+	}
+	if rendered, err := configutil.ParseSingleIPTemplate(result.ClusterAddr); err != nil {
+		return nil, err
+	} else {
+		result.ClusterAddr = rendered
+	}
+
 	sharedConfig, err := configutil.ParseConfig(d)
 	if err != nil {
 		return nil, err
diff --git a/command/server/config_test.go b/command/server/config_test.go
index db6364c83..8ba8d260d 100644
--- a/command/server/config_test.go
+++ b/command/server/config_test.go
@@ -36,6 +36,10 @@ func TestParseListeners(t *testing.T) {
 	testParseListeners(t)
 }
 
+func TestParseSockaddrTemplate(t *testing.T) {
+	testParseSockaddrTemplate(t)
+}
+
 func TestConfigRaftRetryJoin(t *testing.T) {
 	testConfigRaftRetryJoin(t)
 }
diff --git a/command/server/config_test_helpers.go b/command/server/config_test_helpers.go
index 8936a0244..d6c728340 100644
--- a/command/server/config_test_helpers.go
+++ b/command/server/config_test_helpers.go
@@ -843,6 +843,43 @@ listener "tcp" {
 	}
 }
 
+func testParseSockaddrTemplate(t *testing.T) {
+	config, err := ParseConfig(`
+api_addr = <<EOF
+{{- GetAllInterfaces | include "flags" "loopback" | include "type" "ipv4" | attr "address" -}}
+EOF
+listener "tcp" {
+	address = <<EOF
+{{- GetAllInterfaces | include "flags" "loopback" | include "type" "ipv4" | attr "address" -}}:443
+EOF
+	cluster_address = <<EOF
+{{- GetAllInterfaces | include "flags" "loopback" | include "type" "ipv4" | attr "address" -}}:8201
+EOF
+	tls_disable = true
+}`, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expected := &Config{
+		APIAddr: "127.0.0.1",
+		SharedConfig: &configutil.SharedConfig{
+			Listeners: []*configutil.Listener{
+				{
+					Type:           "tcp",
+					Address:        "127.0.0.1:443",
+					ClusterAddress: "127.0.0.1:8201",
+					TLSDisable:     true,
+				},
+			},
+		},
+	}
+	config.Prune()
+	if diff := deep.Equal(config, expected); diff != nil {
+		t.Fatal(diff)
+	}
+}
+
 func testParseSeals(t *testing.T) {
 	config, err := LoadConfigFile("./test-fixtures/config_seals.hcl")
 	if err != nil {
diff --git a/internalshared/configutil/listener.go b/internalshared/configutil/listener.go
index 677dbf9df..64e618489 100644
--- a/internalshared/configutil/listener.go
+++ b/internalshared/configutil/listener.go
@@ -12,6 +12,7 @@ import (
 	"github.com/hashicorp/go-secure-stdlib/strutil"
 	"github.com/hashicorp/go-secure-stdlib/tlsutil"
 	"github.com/hashicorp/go-sockaddr"
+	"github.com/hashicorp/go-sockaddr/template"
 	"github.com/hashicorp/hcl"
 	"github.com/hashicorp/hcl/hcl/ast"
 )
@@ -122,6 +123,16 @@ func ParseListeners(result *SharedConfig, list *ast.ObjectList) error {
 		if err := hcl.DecodeObject(&l, item.Val); err != nil {
 			return multierror.Prefix(err, fmt.Sprintf("listeners.%d:", i))
 		}
+		if rendered, err := ParseSingleIPTemplate(l.Address); err != nil {
+			return multierror.Prefix(err, fmt.Sprintf("listeners.%d:", i))
+		} else {
+			l.Address = rendered
+		}
+		if rendered, err := ParseSingleIPTemplate(l.ClusterAddress); err != nil {
+			return multierror.Prefix(err, fmt.Sprintf("listeners.%d:", i))
+		} else {
+			l.ClusterAddress = rendered
+		}
 
 		// Hacky way, for now, to get the values we want for sanitizing
 		var m map[string]interface{}
@@ -381,3 +392,22 @@ func ParseListeners(result *SharedConfig, list *ast.ObjectList) error {
 
 	return nil
 }
+
+// ParseSingleIPTemplate is used as a helper function to parse out a single IP
+// address from a config parameter.
+func ParseSingleIPTemplate(ipTmpl string) (string, error) {
+	out, err := template.Parse(ipTmpl)
+	if err != nil {
+		return "", fmt.Errorf("unable to parse address template %q: %v", ipTmpl, err)
+	}
+
+	ips := strings.Split(out, " ")
+	switch len(ips) {
+	case 0:
+		return "", errors.New("no addresses found, please configure one")
+	case 1:
+		return strings.TrimSpace(ips[0]), nil
+	default:
+		return "", fmt.Errorf("multiple addresses found (%q), please configure one", out)
+	}
+}
diff --git a/website/content/docs/configuration/listener/tcp.mdx b/website/content/docs/configuration/listener/tcp.mdx
index 90b0b97f9..08cddd118 100644
--- a/website/content/docs/configuration/listener/tcp.mdx
+++ b/website/content/docs/configuration/listener/tcp.mdx
@@ -47,14 +47,18 @@ default value in the `"/sys/config/ui"` [API endpoint](/api/system/config-ui).
 ## `tcp` Listener Parameters
 
 - `address` `(string: "127.0.0.1:8200")` – Specifies the address to bind to for
-  listening.
+  listening.  This can be dynamically defined with a
+  [go-sockaddr template](https://pkg.go.dev/github.com/hashicorp/go-sockaddr/template)
+  that is resolved at runtime.
 
 - `cluster_address` `(string: "127.0.0.1:8201")` – Specifies the address to bind
   to for cluster server-to-server requests. This defaults to one port higher
   than the value of `address`. This does not usually need to be set, but can be
   useful in case Vault servers are isolated from each other in such a way that
   they need to hop through a TCP load balancer or some other scheme in order to
-  talk.
+  talk. This can be dynamically defined with a
+  [go-sockaddr template](https://pkg.go.dev/github.com/hashicorp/go-sockaddr/template)
+  that is resolved at runtime.
 
 - `http_idle_timeout` `(string: "5m")` - Specifies the maximum amount of time to
   wait for the next request when keep-alives are enabled. If `http_idle_timeout`