[installer]: add jaeger sampling options to the tracing object

This also adds the concept of experimental configuration. Mostly,
this is for unsupported SaaS config or things which are useful when
used in a controlled environment. An experimental feature may be
promoted to the main config or dropped without warning.

installer/pkg/common/common.go

@@ -10,10 +10,12 @@ import (
 	"fmt"
 	"io"
 	"math/rand"
+	"strconv"
 	"strings"
 
 	wsk8s "github.com/gitpod-io/gitpod/common-go/kubernetes"
 	config "github.com/gitpod-io/gitpod/installer/pkg/config/v1"
+	"github.com/gitpod-io/gitpod/installer/pkg/config/v1/experimental"
 
 	"github.com/docker/distribution/reference"
 	appsv1 "k8s.io/api/apps/v1"
@@ -79,9 +81,21 @@ func TracingEnv(cfg *config.Config) (res []corev1.EnvVar) {
 		//			 but would make env var composition more cumbersome.
 	}
 
+	samplerType := experimental.TracingSampleTypeConst
+	sampleParam := "1"
+
+	if cfg.Experimental != nil && cfg.Experimental.Observability != nil && cfg.Experimental.Observability.Tracing != nil {
+		if st := cfg.Experimental.Observability.Tracing.SamplerType; st != nil {
+			samplerType = *st
+		}
+		if sp := cfg.Experimental.Observability.Tracing.SamplerParam; sp != nil {
+			sampleParam = strconv.FormatFloat(*sp, 'f', -1, 64)
+		}
+	}
+
 	res = append(res,
-		corev1.EnvVar{Name: "JAEGER_SAMPLER_TYPE", Value: "const"},
-		corev1.EnvVar{Name: "JAEGER_SAMPLER_PARAM", Value: "1"},
+		corev1.EnvVar{Name: "JAEGER_SAMPLER_TYPE", Value: string(samplerType)},
+		corev1.EnvVar{Name: "JAEGER_SAMPLER_PARAM", Value: sampleParam},
 	)
 
 	return

installer/pkg/config/v1/config.go

@@ -6,6 +6,7 @@ package config
 
 import (
 	"github.com/gitpod-io/gitpod/installer/pkg/config"
+	"github.com/gitpod-io/gitpod/installer/pkg/config/v1/experimental"
 	"github.com/gitpod-io/gitpod/ws-daemon/pkg/resources"
 
 	corev1 "k8s.io/api/core/v1"
@@ -86,6 +87,11 @@ type Config struct {
 	License       *ObjectRef    `json:"license,omitempty"`
 
 	SSHGatewayHostKey *ObjectRef `json:"sshGatewayHostKey,omitempty"`
+
+	// Anything in here is provided as a convenience, but is entirely unsupported
+	//
+	// HERE BE DRAGONS! Enter at your own risk
+	Experimental *experimental.Config `json:"experimental,omitempty"`
 }
 
 type Metadata struct {

installer/pkg/config/v1/experimental/config.go

@@ -0,0 +1,28 @@
+// Copyright (c) 2022 Gitpod GmbH. All rights reserved.
+// Licensed under the GNU Affero General Public License (AGPL).
+// See License-AGPL.txt in the project root for license information.
+
+package experimental
+
+type Config struct {
+	Observability *Observability `json:"observability"`
+}
+
+type Observability struct {
+	Tracing *Tracing `json:"tracing,omitempty"`
+}
+
+type Tracing struct {
+	SamplerType  *TracingSampleType `json:"samplerType,omitempty" validate:"omitempty,tracing_sampler_type"`
+	SamplerParam *float64           `json:"samplerParam,omitEmpty" validate:"required_with=SamplerType"`
+}
+
+type TracingSampleType string
+
+// Values taken from https://github.com/jaegertracing/jaeger-client-go/blob/967f9c36f0fa5a2617c9a0993b03f9a3279fadc8/config/config.go#L71
+const (
+	TracingSampleTypeConst         TracingSampleType = "const"
+	TracingSampleTypeProbabilistic TracingSampleType = "probabilistic"
+	TracingSampleTypeRateLimiting  TracingSampleType = "rateLimiting"
+	TracingSampleTypeRemote        TracingSampleType = "remote"
+)

installer/pkg/config/v1/experimental/validation.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2022 Gitpod GmbH. All rights reserved.
+// Licensed under the GNU Affero General Public License (AGPL).
+// See License-AGPL.txt in the project root for license information.
+
+package experimental
+
+import "github.com/go-playground/validator/v10"
+
+var TracingSampleTypeList = map[TracingSampleType]struct{}{
+	TracingSampleTypeConst:         {},
+	TracingSampleTypeProbabilistic: {},
+	TracingSampleTypeRateLimiting:  {},
+	TracingSampleTypeRemote:        {},
+}
+
+var ValidationChecks = map[string]validator.Func{
+	"tracing_sampler_type": func(fl validator.FieldLevel) bool {
+		_, ok := TracingSampleTypeList[TracingSampleType(fl.Field().String())]
+		return ok
+	},
+}

installer/pkg/config/v1/validation.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 
 	"github.com/gitpod-io/gitpod/installer/pkg/cluster"
+	"github.com/gitpod-io/gitpod/installer/pkg/config/v1/experimental"
 	"golang.org/x/crypto/ssh"
 	"sigs.k8s.io/yaml"
 
@@ -60,6 +61,11 @@ func (v version) LoadValidationFuncs(validate *validator.Validate) error {
 			return ok
 		},
 	}
+
+	for k, v := range experimental.ValidationChecks {
+		funcs[k] = v
+	}
+
 	for n, f := range funcs {
 		err := validate.RegisterValidation(n, f)
 		if err != nil {