{"id":41495,"date":"2023-12-01T05:27:26","date_gmt":"2023-12-01T05:27:26","guid":{"rendered":"https:\/\/www.devopsschool.com\/blog\/?p=41495"},"modified":"2025-01-13T12:15:19","modified_gmt":"2025-01-13T12:15:19","slug":"knative-tutorials-chapter-10-knative-tutorials-servicing-workflow-between-components","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/knative-tutorials-chapter-10-knative-tutorials-servicing-workflow-between-components\/","title":{"rendered":"Knative Tutorials – Chapter – 10 – Knative Tutorials: servicing workflow between Components"},"content":{"rendered":"\n
    \n
  1. Request Initiation<\/strong>:\n
      \n
    • A user sends a request to an application hosted on Knative.<\/li>\n\n\n\n
    • This request first hits the Istio Ingress Gateway<\/code>, which is the entry point for external traffic into the Kubernetes cluster.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
    • VirtualService Routing<\/strong>:\n
        \n
      • The Istio Ingress Gateway<\/code> uses Istio VirtualService<\/code> to determine where to route the request. Knative sets up these VirtualServices when a service is created or updated.<\/li>\n\n\n\n
      • Typically, the VirtualService<\/code> will point to the Knative Activator<\/code> when the application is scaled to zero or during scaling up from zero.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
      • Activator<\/strong>:\n
          \n
        • The Activator<\/code> is responsible for starting up instances of the application (Pods) when there are none running. It plays a crucial role in scale-to-zero functionality.<\/li>\n\n\n\n
        • If an application is scaled to zero (no active pods), the Activator<\/code> receives the incoming request, triggers the Kubernetes deployment to start a new pod, and then buffers incoming requests until the pod is ready to handle them.<\/li>\n\n\n\n
        • Once the pod is running and ready, the Activator<\/code> forwards the buffered requests to the pod.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
        • Autoscaler<\/strong>:\n
            \n
          • The Autoscaler<\/code> component in Knative observes traffic load and scales the application pods up or down based on the configuration (like concurrency-based metrics) and actual traffic.<\/li>\n\n\n\n
          • It receives metrics about ongoing traffic and makes decisions on when to scale. The Activator<\/code> also plays a part in this by sending metrics to the Autoscaler<\/code> when it’s buffering requests for scaled-to-zero applications.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
          • Knative Service and Revisions<\/strong>:\n
              \n
            • In Knative, when you create a Service<\/code> (not to be confused with Kubernetes Service), it represents a specific configuration of your application.<\/li>\n\n\n\n
            • Each time you modify the Service<\/code>, Knative creates a new Revision<\/code>. Each Revision<\/code> is a snapshot of the code and configurations for a particular version of the service.<\/li>\n\n\n\n
            • The actual running code is encapsulated in a Kubernetes deployment associated with that Revision<\/code>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
            • Knative Route<\/strong>:\n
                \n
              • The Route<\/code> is responsible for determining which Revision<\/code> of a Service<\/code> receives traffic. You can set up the Route<\/code> to split traffic between multiple Revisions<\/code> for blue-green deployments, canary releases, etc.<\/li>\n\n\n\n
              • Combined with VirtualService<\/code>, it ensures the right revisions of your application are being routed traffic.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
              • Request Completion<\/strong>:\n
                  \n
                • After the application processes the request, the response travels back through the same path: from the pod to (possibly) the Activator<\/code>, and then out through the Istio Ingress Gateway<\/code> to the user.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":"","_joinchat":[],"footnotes":""},"categories":[8921],"tags":[],"class_list":["post-41495","post","type-post","status-publish","format-standard","hentry","category-knative"],"_links":{"self":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/41495","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/comments?post=41495"}],"version-history":[{"count":1,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/41495\/revisions"}],"predecessor-version":[{"id":41496,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/41495\/revisions\/41496"}],"wp:attachment":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/media?parent=41495"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/categories?post=41495"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/tags?post=41495"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}