add session affinity support for weighted routing with istio

Add `.spec.analysis.sessionAffinity` to configure session affinity for
weighted routing. Add support for session affinity in the Istio router,
using the `Set-Cookie` and `Cookie` headers.

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

pkg/apis/flagger/v1beta1/canary.go

@@ -262,6 +262,20 @@ type CanaryAnalysis struct {
 	// A/B testing HTTP header match conditions
 	// +optional
 	Match []istiov1alpha3.HTTPMatchRequest `json:"match,omitempty"`
+
+	// SessionAffinity represents the session affinity settings for a canary run.
+	// +optional
+	SessionAffinity *SessionAffinity `json:"sessionAffinity,omitempty"`
+}
+
+type SessionAffinity struct {
+	// CookieName is the key that will be used for the session affinity cookie.
+	CookieName string `json:"cookieName,omitempty"`
+	// MaxAge indicates the number of seconds until the session affinity cookie will expire.
+	// ref: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie#attributes
+	// The default value is 86,400 seconds, i.e. a day.
+	// +optional
+	MaxAge int `json:"maxAge,omitempty"`
 }
 
 // CanaryMetric holds the reference to metrics used for canary analysis
@@ -437,6 +451,15 @@ type CustomMetadata struct {
 	Annotations map[string]string `json:"annotations,omitempty"`
 }
 
+// GetMaxAge returns the max age of a cookie in seconds.
+func (s *SessionAffinity) GetMaxAge() int {
+	if s.MaxAge == 0 {
+		// 24 hours * 60 mins * 60 seconds
+		return 86400
+	}
+	return s.MaxAge
+}
+
 // GetServiceNames returns the apex, primary and canary Kubernetes service names
 func (c *Canary) GetServiceNames() (apexName, primaryName, canaryName string) {
 	apexName = c.Spec.TargetRef.Name

pkg/apis/flagger/v1beta1/status.go

@@ -74,6 +74,10 @@ type CanaryStatus struct {
 	CanaryWeight int         `json:"canaryWeight"`
 	Iterations   int         `json:"iterations"`
 	// +optional
+	PreviousSessionAffinityCookie string `json:"previousSessionAffinityCookie,omitempty"`
+	// +optional
+	SessionAffinityCookie string `json:"sessionAffinityCookie,omitempty"`
+	// +optional
 	TrackedConfigs *map[string]string `json:"trackedConfigs,omitempty"`
 	// +optional
 	LastAppliedSpec string `json:"lastAppliedSpec,omitempty"`

pkg/apis/flagger/v1beta1/zz_generated.deepcopy.go

@@ -263,6 +263,11 @@ func (in *CanaryAnalysis) DeepCopyInto(out *CanaryAnalysis) {
 			(*in)[i].DeepCopyInto(&(*out)[i])
 		}
 	}
+	if in.SessionAffinity != nil {
+		in, out := &in.SessionAffinity, &out.SessionAffinity
+		*out = new(SessionAffinity)
+		**out = **in
+	}
 	return
 }
 
@@ -815,3 +820,19 @@ func (in *MetricTemplateStatus) DeepCopy() *MetricTemplateStatus {
 	in.DeepCopyInto(out)
 	return out
 }
+
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *SessionAffinity) DeepCopyInto(out *SessionAffinity) {
+	*out = *in
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new SessionAffinity.
+func (in *SessionAffinity) DeepCopy() *SessionAffinity {
+	if in == nil {
+		return nil
+	}
+	out := new(SessionAffinity)
+	in.DeepCopyInto(out)
+	return out
+}