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https://issues.apache.org/jira/browse/FLINK-16602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17059706#comment-17059706
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Yang Wang commented on FLINK-16602:
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[~felixzheng] Thanks for creating this ticket and share your thoughts about the
service. I will address the issues one by one.
> boundary of the two Services
In my original design, the rest service is optional and used for accessing the
dashboard/rest server outside of the K8s cluster. So only rest port is
necessary. We always need to expose the rest port on the internal service.
Because when you have deployer running in the K8s, which will be used to start
Flink cluster and proxy webui, the internal service will be used to forward the
webui traffic to jobmanager.
I prefer the current behavior and do not think the boundary of the two services
is not clear.
> Do not create the internal Service in the high availability case
We will have the same situation as above when using the deployer. Using the
service is easier to forward traffic to rest server. Moreover, i think there is
no harm to leave the internal service there.
> Use headless for internal service
Using the headless is good choice to reduce the pressure of kube proxy. If we
use ipvs, it will not be a urgent problem. Also using headless service will
cause some dns cache problem when the jobmanager failover. Since hostname do
not change, the corresponding IP address changes. I am not sure about this, but
i think there is such risk. So in my original design, i choose ClusterIP
instead of headless service.
> Rework the Service design for Kubernetes deployment
> ---------------------------------------------------
>
> Key: FLINK-16602
> URL: https://issues.apache.org/jira/browse/FLINK-16602
> Project: Flink
> Issue Type: Improvement
> Components: Deployment / Kubernetes
> Affects Versions: 1.10.0
> Reporter: Canbin Zheng
> Priority: Major
> Fix For: 1.11.0
>
>
> {color:#0e101a}At the moment we usually create two Services for a Flink
> application, one is the internal Service and the other is the so-called rest
> Service, the previous aims for forwarding request from the TMs to the JM, and
> the rest Service mainly serves as an external service for the Flink
> application. Here is a summary of the issues:{color}
> # {color:#0e101a}The functionality boundary of the two Services is not clear
> enough since the internal Service could also become the rest Service when its
> exposed type is ClusterIP.{color}
> # {color:#0e101a}For the high availability scenario, we create a useless
> internal Service which does not help forward the internal requests since the
> TMs directly communicate with the JM via the IP or hostname of the JM
> Pod.{color}
> # {color:#0e101a}Headless service is enough to help forward the internal
> requests from the TMs to the JM. Service of ClusterIP type would add
> corresponding rules into the iptables, too many rules in the iptables would
> lower the kube-proxy's efficiency in refreshing iptables while notified of
> change events, which could possibly cause severe stability problems in a
> Kubernetes cluster.{color}
>
> {color:#0e101a}Therefore, we propose some improvements to the current
> design:{color}
> # {color:#0e101a}Clarify the functionality boundary for the two Services,
> the internal Service only serves the internal communication from TMs to JM,
> while the rest Service makes the Flink cluster accessible from outside. The
> internal Service only exposes the RPC and BLOB ports while the external one
> exposes the REST port.{color}
> # {color:#0e101a}Do not create the internal Service in the high availability
> case.{color}
> # {color:#0e101a}Use HEADLESS type for the internal Service.{color}
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