add headers config key

`headers` config key defines an unlimited number of http headers in a multi-line annotation or configmap option. Its advantage over `config-backend` is the support of variables, currently `%[service]` and `%[namespace]`.

docs/content/en/docs/configuration/keys.md

@@ -148,6 +148,7 @@ The table below describes all supported configuration keys.
 | [`dynamic-scaling`](#dynamic-scaling)                | [true\|false]                           | Backend | `true`             |
 | [`forwardfor`](#forwardfor)                          | [add\|ignore\|ifmissing]                | Global  | `add`              |
 | [`fronting-proxy-port`](#fronting-proxy-port)        | port number                             | Global  | 0 (do not listen)  |
+| [`headers`](#headers)                                | multiline header:value pair             | Backend |                    |
 | [`health-check-addr`](#health-check)                 | address for health checks               | Backend |                    |
 | [`health-check-fall-count`](#health-check)           | number of failures                      | Backend |                    |
 | [`health-check-interval`](#health-check)             | time with suffix                        | Backend |                    |
@@ -963,6 +964,28 @@ See also:
 * [Bind](#bind)
 * [Bind port](#bind-port)
 
+## Headers
+
+| Configuration key | Scope     | Default | Since  |
+|-------------------|-----------|---------|--------|
+| `headers`         | `Backend` |         | v0.11  |
+
+Configures a list of HTTP header names and the value it should be configured with. More than one header can be configured using a multi-line configuration value. The name of the header and its value should be separated with a colon and/or any amount of spaces.
+
+The following variables can be used in the value:
+
+* `%[namespace]`: namespace of the ingress or service
+* `%[service]`: name of the service which received the request
+
+Configuration example:
+
+```yaml
+    annotations:
+      ingress.kubernetes.io/headers: |
+        x-path: /
+        host: %[service].%[namespace].svc.cluster.local
+```
+
 ---
 
 ## Health check

pkg/converters/ingress/annotations/backend.go

@@ -490,6 +490,33 @@ func (c *updater) buildBackendHealthCheck(d *backData) {
 	d.backend.HealthCheck.URI = d.mapper.Get(ingtypes.BackHealthCheckURI).Value
 }
 
+func (c *updater) buildBackendHeaders(d *backData) {
+	headers := d.mapper.Get(ingtypes.BackHeaders)
+	if headers.Value == "" {
+		return
+	}
+	for _, header := range utils.LineToSlice(headers.Value) {
+		header = strings.TrimSpace(header)
+		if header == "" {
+			continue
+		}
+		idx := strings.IndexAny(header, ": ")
+		if idx <= 0 {
+			c.logger.Warn("ignored missing header name or value on %v: %s", headers.Source, header)
+			continue
+		}
+		name := strings.TrimRight(header[:idx], ":")
+		value := strings.TrimSpace(header[idx+1:])
+		// TODO this should use a structured type and a smart match/replace if growing a bit more
+		value = strings.ReplaceAll(value, "%[service]", d.backend.Name)
+		value = strings.ReplaceAll(value, "%[namespace]", d.backend.Namespace)
+		d.backend.Headers = append(d.backend.Headers, &hatypes.BackendHeader{
+			Name:  name,
+			Value: value,
+		})
+	}
+}
+
 func (c *updater) buildBackendHSTS(d *backData) {
 	rawHSTSList := d.mapper.GetBackendConfig(
 		d.backend,

pkg/converters/ingress/annotations/backend_test.go

@@ -911,6 +911,77 @@ func TestCors(t *testing.T) {
 	}
 }
 
+func TestHeaders(t *testing.T) {
+	testCases := []struct {
+		headers  string
+		expected []*hatypes.BackendHeader
+		logging  string
+	}{
+		// 0
+		{
+			headers: `invalid`,
+			logging: `WARN ignored missing header name or value on ingress 'ing1/app': invalid`,
+		},
+		// 1
+		{
+			headers: `key value`,
+			expected: []*hatypes.BackendHeader{
+				{Name: "key", Value: "value"},
+			},
+		},
+		// 2
+		{
+			headers: `name: content`,
+			expected: []*hatypes.BackendHeader{
+				{Name: "name", Value: "content"},
+			},
+		},
+		// 3
+		{
+			headers: `k:v`,
+			expected: []*hatypes.BackendHeader{
+				{Name: "k", Value: "v"},
+			},
+		},
+		// 4
+		{
+			headers: `host: %[service].%[namespace].svc.cluster.local`,
+			expected: []*hatypes.BackendHeader{
+				{Name: "host", Value: "app.default.svc.cluster.local"},
+			},
+		},
+		// 5
+		{
+			headers: `
+k8snamespace: %[namespace]
+k8sservice: %[service]
+host: %[service].%[namespace].svc.cluster.local
+`,
+			expected: []*hatypes.BackendHeader{
+				{Name: "k8snamespace", Value: "default"},
+				{Name: "k8sservice", Value: "app"},
+				{Name: "host", Value: "app.default.svc.cluster.local"},
+			},
+		},
+	}
+	source := &Source{
+		Namespace: "ing1",
+		Name:      "app",
+		Type:      "ingress",
+	}
+	for i, test := range testCases {
+		c := setup(t)
+		ann := map[string]map[string]string{
+			"/": {ingtypes.BackHeaders: test.headers},
+		}
+		d := c.createBackendMappingData("default/app", source, map[string]string{}, ann, []string{"/"})
+		c.createUpdater().buildBackendHeaders(d)
+		c.compareObjects("headers", i, d.backend.Headers, test.expected)
+		c.logger.CompareLogging(test.logging)
+		c.teardown()
+	}
+}
+
 func TestHSTS(t *testing.T) {
 	testCases := []struct {
 		paths      []string

pkg/converters/ingress/annotations/updater.go

@@ -165,6 +165,7 @@ func (c *updater) UpdateBackendConfig(backend *hatypes.Backend, mapper *Mapper)
 	c.buildBackendDNS(data)
 	c.buildBackendDynamic(data)
 	c.buildBackendAgentCheck(data)
+	c.buildBackendHeaders(data)
 	c.buildBackendHealthCheck(data)
 	c.buildBackendHSTS(data)
 	c.buildBackendLimit(data)

pkg/converters/ingress/types/annotations.go

@@ -78,6 +78,7 @@ const (
 	BackCorsExposeHeaders      = "cors-expose-headers"
 	BackCorsMaxAge             = "cors-max-age"
 	BackDynamicScaling         = "dynamic-scaling"
+	BackHeaders                = "headers"
 	BackHealthCheckAddr        = "health-check-addr"
 	BackHealthCheckFallCount   = "health-check-fall-count"
 	BackHealthCheckInterval    = "health-check-interval"

pkg/haproxy/instance_test.go

@@ -326,6 +326,26 @@ func TestBackends(t *testing.T) {
     # path02 = d1.local/app
     http-request set-var(txn.pathID) base,lower,map_beg(/etc/haproxy/maps/_back_d1_app_8080_idpath.map)
     http-request use-service lua.send-413 if { var(txn.pathID) path02 } { req.body_size,sub(2048) gt 0 }`,
+		},
+		{
+			doconfig: func(g *hatypes.Global, h *hatypes.Host, b *hatypes.Backend) {
+				b.Headers = []*hatypes.BackendHeader{
+					{Name: "Name", Value: "Value"},
+				}
+			},
+			expected: `
+    http-request set-header Name Value`,
+		},
+		{
+			doconfig: func(g *hatypes.Global, h *hatypes.Host, b *hatypes.Backend) {
+				b.Headers = []*hatypes.BackendHeader{
+					{Name: "X-ID", Value: "abc"},
+					{Name: "Host", Value: "app.domain"},
+				}
+			},
+			expected: `
+    http-request set-header X-ID abc
+    http-request set-header Host app.domain`,
 		},
 		{
 			doconfig: func(g *hatypes.Global, h *hatypes.Host, b *hatypes.Backend) {

pkg/haproxy/types/backend.go

@@ -262,6 +262,11 @@ func (p *BackendPath) String() string {
 	return fmt.Sprintf("%+v", *p)
 }
 
+// String ...
+func (h *BackendHeader) String() string {
+	return fmt.Sprintf("%+v", *h)
+}
+
 // String ...
 func (b *BackendConfigAuth) String() string {
 	return fmt.Sprintf("%+v", *b)

pkg/haproxy/types/types.go

@@ -383,6 +383,7 @@ type Backend struct {
 	Cookie           Cookie
 	CustomConfig     []string
 	Dynamic          DynBackendConfig
+	Headers          []*BackendHeader
 	HealthCheck      HealthCheck
 	Limit            BackendLimit
 	ModeTCP          bool
@@ -455,6 +456,12 @@ type BackendPath struct {
 	Path     string
 }
 
+// BackendHeader ...
+type BackendHeader struct {
+	Name  string
+	Value string
+}
+
 // BackendConfigBool ...
 type BackendConfigBool struct {
 	Paths  BackendPaths

rootfs/etc/haproxy/template/haproxy.tmpl

@@ -378,6 +378,11 @@ backend {{ $backend.ID }}
 {{- end }}
 {{- end }}
 
+{{- /*------------------------------------*/}}
+{{- range $header := $backend.Headers }}
+    http-request set-header {{ $header.Name }} {{ $header.Value }}
+{{- end }}
+
 {{- /*------------------------------------*/}}
 {{- if $backend.TLS.HasTLSAuth }}
 {{- $needSSLACL := not $backend.HasSSLRedirect }}