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73 lines
3.6 KiB
Markdown
73 lines
3.6 KiB
Markdown
# Reaching the API
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## Ports and IPs Served On
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The Kubernetes API is served by the Kubernetes APIServer process. Typically,
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there is one of these running on a single kubernetes-master node.
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By default the Kubernetes APIserver serves
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HTTP on 3 ports:
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1. Localhost Port
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- serves HTTP
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- default is port 8080, change with `-port` flag.
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- defaults IP is localhost, change with `-address` flag.
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- no authentication or authorization checks in HTTP
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- protected by need to have host access
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2. ReadOnly Port
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- default is port 7080, change with `-read_only_port`
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- default IP is first non-localhost network interface, change with `-public_address_override`
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- serves HTTP
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- no authentication checks in HTTP
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- only GET requests are allowed.
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- requests are rate limited
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3. Secure Port
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- default is port 6443, change with `-secure_port`
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- default IP is first non-localhost network interface, change with `-public_address_override`
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- serves HTTPS. Set cert with `-tls_cert_file` and key with `-tls_private_key_file`.
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- uses token-file based [authentication](./authentication.md).
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- uses policy-based [authorization](./authorization.md).
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## Proxies and Firewall rules
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Additionally, in typical configurations (i.e. GCE), there is a proxy (nginx) running
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on the same machine as the apiserver process. The proxy serves HTTPS protected
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by Basic Auth on port 443, and proxies to the apiserver on localhost:8080.
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Typically, firewall rules will allow HTTPS access to port 443.
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The above are defaults and reflect how Kubernetes is deployed to GCE using
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kube-up.sh. Other cloud providers may vary.
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## Use Cases vs IP:Ports
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There are three differently configured serving ports because there are a
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variety of uses cases:
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1. Clients outside of a Kubernetes cluster, such as human running `kubectl`
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on desktop machine. Currently, accesses the Localhost Port via a proxy (nginx)
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running on the `kubernetes-master` machine. Proxy uses Basic Auth.
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2. Processes running in Containers on Kubernetes that need to do read from
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the apiserver. Currently, these can use Readonly Port.
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3. Scheduler and Controller-manager processes, which need to do read-write
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API operations. Currently, these have to run on the
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operations on the apiserver. Currently, these have to run on the same
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host as the apiserver and use the Localhost Port.
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4. Kubelets, which need to do read-write API operations and are necessarily
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on different machines than the apiserver. Kubelet uses the Secure Port
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to get their pods, to find the services that a pod can see, and to
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write events. Credentials are distributed to kubelets at cluster
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setup time.
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## Expected changes
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- Policy will limit the actions kubelets can do via the authed port.
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- Kube-proxy currently uses the readonly port to read services and endpoints,
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but will eventually use the auth port.
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- Kubelets may change from token-based authentication to cert-based-auth.
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- Scheduler and Controller-manager will use the Secure Port too. They
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will then be able to run on different machines than the apiserver.
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- A general mechanism will be provided for [giving credentials to
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pods](
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https://github.com/GoogleCloudPlatform/kubernetes/issues/1907).
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- The Readonly Port will no longer be needed and will be removed.
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- Clients, like kubectl, will all support token-based auth, and the
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Localhost will no longer be needed, and will not be the default.
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However, the localhost port may continue to be an option for
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installations that want to do their own auth proxy.
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