BK8s datasource middleware -- PoC for A records (#153)

* Laying down kubernetes middleware foundation

* Duplicated a bunch of code form etcd middleware
* Duplicated code hacked to compile and load as a separate middleware

* Adding verbose build option to Makefile

* Removing stubzone and tls support

tls and stubzone support was carried over from base etcd middleware code.
Removing to simplify the kube middleware implementation. (For now.)

* Adding conf directory for sample conf files

* Removing stubzone support from query handler

* Remove upstream and proxy from k8s corefile.

Not sure that upstream or proxy makes sense for a k8s backed zone.

* Comment out use of singleflight serialization

* Removing parsing support for "upstream" directive from k8s

* Removing upstream directive parsing code

* Removing CNAME and TXT lookup implementation

* Create README.md

Brain-dump of DNS record name assembly and open work items.

* Adding notes about wildcard handling

* Adding basic k8s API client

* Fleshing out methods on k8s connector

* Remove PathPrefix from middleware init

* Removing incorrect plural

* Adding brute-force k8s service lookup functions

* Initializing k8s API connector during startup

* Hacking around to call k8s connector

* Parsing incoming domain name into serviceName and namespace

* Improving and simplifying k8s zone matching and label segmentation

* Removing unused functions carried over from etcd middleware

* Adding basic return of k8s data to DNS client

* updated debugging println statements to flag with "[debug]"
* removed code in kubernetes.go::Records that was a hold-over from etcd middleware.
* Removed some random exploratory hacking.

* Minior README.md updates

* Updating with demo instructions

* Updating README.md with CoreFile and removing completed TODO items

* Updating conf file and README to reflect DNS response cache works

* Disabling DNS response caching

* Adding debug statement on entry to Records()

* Changing port number in exampes to port 53.

* Misc style and clarity changes

* Removing empty function definitions

* Adding comment to track future cleanup

* Refactoring README to follow style of other middleware

* Exposing dataobject field (typo)

middleware/kubernetes/k8sclient/dataobjects.go

@@ -0,0 +1,110 @@
+package k8sclient
+
+import (
+    "encoding/json"
+    "net/http"
+)
+
+
+func getJson(url string, target interface{}) error {
+    r, err := http.Get(url)
+    if err != nil {
+        return err
+    }
+    defer r.Body.Close()
+
+    return json.NewDecoder(r.Body).Decode(target)
+}
+
+
+// Kubernetes Resource List
+type ResourceList struct {
+    Kind         string `json:"kind"`
+    GroupVersion string `json:"groupVersion"`
+    Resources    []resource `json:"resources"`
+}
+
+type resource struct {
+    Name         string `json:"name"`
+    Namespaced   bool   `json:"namespaced"`
+    Kind         string `json:"kind"`
+}
+
+
+// Kubernetes NamespaceList
+type NamespaceList struct {
+    Kind         string          `json:"kind"`
+    APIVersion   string          `json:"apiVersion"`
+    Metadata     apiListMetadata  `json:"metadata"`
+    Items        []nsItems       `json:"items"`   
+}
+
+type apiListMetadata struct {
+    SelfLink         string `json:"selfLink"`
+    resourceVersion  string `json:"resourceVersion"`
+}
+
+type nsItems struct {
+    Metadata   nsMetadata  `json:"metadata"`
+    Spec       nsSpec      `json:"spec"`
+    Status     nsStatus    `json:"status"`
+}
+
+type nsMetadata struct {
+    Name              string  `json:"name"`
+    SelfLink          string  `json:"selfLink"`
+    Uid               string  `json:"uid"`
+    ResourceVersion   string  `json:"resourceVersion"`
+    CreationTimestamp string  `json:"creationTimestamp"`
+}
+
+type nsSpec struct {
+    Finalizers []string `json:"finalizers"`
+}
+
+type nsStatus struct {
+    Phase string `json:"phase"`
+}
+
+
+// Kubernetes ServiceList
+type ServiceList struct {
+    Kind         string          `json:"kind"`
+    APIVersion   string          `json:"apiVersion"`
+    Metadata     apiListMetadata  `json:"metadata"`
+    Items        []ServiceItem    `json:"items"`   
+}
+
+type ServiceItem struct {
+    Metadata   serviceMetadata  `json:"metadata"`
+    Spec       serviceSpec      `json:"spec"`
+//    Status     serviceStatus    `json:"status"`
+}
+
+type serviceMetadata struct {
+    Name              string  `json:"name"`
+    Namespace         string  `json:"namespace"`
+    SelfLink          string  `json:"selfLink"`
+    Uid               string  `json:"uid"`
+    ResourceVersion   string  `json:"resourceVersion"`
+    CreationTimestamp string  `json:"creationTimestamp"`
+    // labels
+}
+
+type serviceSpec struct {
+    Ports           []servicePort `json:"ports"`
+    ClusterIP       string        `json:"clusterIP"`
+    Type            string        `json:"type"`
+    SessionAffinity string        `json:"sessionAffinity"`
+}
+
+type servicePort struct {
+    Name            string        `json:"name"`
+    Protocol        string        `json:"protocol"`
+    Port            int           `json:"port"`
+    TargetPort      int           `json:"targetPort"`
+}
+
+type serviceStatus struct {
+    LoadBalancer string `json:"loadBalancer"`
+}

middleware/kubernetes/k8sclient/k8sclient.go

@@ -0,0 +1,117 @@
+package k8sclient
+
+import (
+//    "fmt"
+    "net/url"
+)
+
+// API strings
+const (
+    apiBase       = "/api/v1"
+    apiNamespaces = "/namespaces"
+    apiServices   = "/services"
+)
+
+// Defaults
+const (
+    defaultBaseUrl = "http://localhost:8080"
+)
+
+
+type K8sConnector struct {
+    baseUrl string
+}
+
+func (c *K8sConnector) SetBaseUrl(u string) error {
+    validUrl, error := url.Parse(u)
+
+    if error != nil {
+        return error
+    }
+    c.baseUrl = validUrl.String()
+
+    return nil
+}
+
+func (c *K8sConnector) GetBaseUrl() string {
+    return c.baseUrl
+}
+
+
+func (c *K8sConnector) GetResourceList() *ResourceList {
+    resources := new(ResourceList)
+    
+    error := getJson((c.baseUrl + apiBase), resources)
+    if error != nil {
+        return nil
+    }
+
+    return resources
+}
+
+
+func (c *K8sConnector) GetNamespaceList() *NamespaceList {
+    namespaces := new(NamespaceList)
+
+    error := getJson((c.baseUrl + apiBase + apiNamespaces), namespaces)
+    if error != nil {
+        return nil
+    }
+
+    return namespaces
+}
+
+
+func (c *K8sConnector) GetServiceList() *ServiceList {
+    services := new(ServiceList)
+
+    error := getJson((c.baseUrl + apiBase + apiServices), services)
+    if error != nil {
+        return nil
+    }
+
+    return services
+}
+
+
+func (c *K8sConnector) GetServicesByNamespace() map[string][]ServiceItem {
+     // GetServicesByNamespace returns a map of namespacename :: [ kubernetesServiceItem ]
+
+    items := make(map[string][]ServiceItem)
+
+    k8sServiceList := c.GetServiceList()
+    k8sItemList := k8sServiceList.Items
+
+    for _, i := range k8sItemList {
+        namespace := i.Metadata.Namespace
+        items[namespace] = append(items[namespace], i)
+    }
+
+    return items
+}
+
+
+func (c *K8sConnector) GetServiceItemInNamespace(namespace string, servicename string) *ServiceItem {
+    // GetServiceItemInNamespace returns the ServiceItem that matches servicename in the namespace
+
+    itemMap := c.GetServicesByNamespace()
+
+    // TODO: Handle case where namesapce == nil
+
+    for _, x := range itemMap[namespace] {
+        if x.Metadata.Name == servicename {
+            return &x
+        }
+    }
+
+    // No matching item found in namespace
+    return nil
+}
+
+
+func NewK8sConnector(baseurl string) *K8sConnector {
+    k := new(K8sConnector)
+    k.SetBaseUrl(baseurl)
+
+    return k
+}