Service located in another namespace

Question

I have been trying to find a way to define a service in one namespace that links to a Pod running in another namespace   I know that containers in a Pod running in namespaceA can access serviceX defined in namespaceB by referencing it in the cluster DNS as serviceX namespaceB svc cluster local  but I would rather not have the code inside the container need to know about the location of serviceX   That is  I want the code to just lookup serviceX and then be able to access it   The Kubernetes documentation suggests that this is possible   It says that one of the reasons that you would define a service without a selector is that You want to point your service to a service in another Namespace or on another cluster   That suggests to me that I should    Define a serviceX service in namespaceA  without a selector  since the POD I want to select isn t in namespaceA   Define a service  which I also called serviceX  in namespaceB  and then Define an Endpoints object in namespaceA to point to serviceX in namespaceB    It is this third step that I have not been able to accomplish   First  I tried defining the Endpoints object this way   kind  Endpoints apiVersion  v1 metadata    name  serviceX   namespace  namespaceA subsets    - addresses        - targetRef            kind  Service           namespace  namespaceB           name  serviceX           apiVersion  v1     ports        - name  http         port  3000   That seemed the logical approach  and obviously what the targetRef was for    But  this led to an error saying that the ip field in the addresses array was mandatory   So  my next try was to assign a fixed ClusterIP address to serviceX in namespaceB  and put that in the IP field  note that the service cluster ip range is configured as 192 168 0 0 16  and 192 168 1 1 was assigned as the ClusterIP for serviceX in namespaceB  serviceX in namespaceA was auto assigned a different ClusterIP on the 192 168 0 0 16 subnet    kind  Endpoints apiVersion  v1 metadata    name  serviceX   namespace  namespaceA subsets    - addresses          - ip  192 168 1 1           targetRef              kind  Service             namespace  namespaceB             name  serviceX             apiVersion  v1     ports        - name  http         port  3000   That was accepted  but accesses to serviceX in namespaceA did not get forwarded to the Pod in namespaceB - they timed out   Looking at the iptables setup  it looks like it would have had to do NAT pre-routing twice to accomplish that   The only thing I did find that worked - but is not a satisfactory solution - is to lookup the actual IP address of the Pod providing serviceX in namespaceB and put that address in the Endpoints object in namespaceA   That isn t satisfactory  of course  because the Pod IP address may change over time   That s the problem service IPs are there to solve   So  is there a way to meet what seems to be the promise of the documentation that I can point a service in one namespace to a service running in a different namespace   A commenter questioned why you would want to do this - here is a use case that makes sense to me  at least   Say you have a multi-tenant system  which also includes a common data-access function that can be shared between tenants   Now imagine that there are different flavors of this data-access function with common APIs  but different performance characteristics   Some tenants get access to one of them  other tenants have access to another one   Each tenant s pods run in their own namespaces  but each one needs to access one of these common data-access services  which will necessarily be in another namespace  since it is accessed by multiple tenants    But  you wouldn t want the tenant to have to change their code if their subscription changes to access the higher-performing service   A potential solution  the cleanest one I can think of  if only it worked  is to include a service definition in each tenant s namespace for the data-access service  with each one configured for the appropriate endpoint   This service definition would be configured to point to the proper data-access service each tenant is entitled to use

User · Answer

It is so simple to do it

if you want to use it as host and want to resolve it

If you are using ambassador to any other API gateway for service located in another namespace it's always suggested to use :

            Use : <service name>
            Use : <service.name>.<namespace name>
            Not : <service.name>.<namespace name>.svc.cluster.local

it will be like : servicename.namespacename.svc.cluster.local

this will send request to a particular service inside the namespace you have mention.

example:

kind: Service
apiVersion: v1
metadata:
  name: service
spec:
  type: ExternalName
  externalName: <servicename>.<namespace>.svc.cluster.local

Here replace the <servicename> and <namespace> with the appropriate value.

In Kubernetes, namespaces are used to create virtual environment but all are connect with each other.

User · Answer

To access services in two different namespaces you can use url like this  HTTP    lt your-service-name gt   lt namespace-with-that-service gt  svc cluster local  To list out all your namespaces you can use  kubectl get namespace  And for service in that namespace you can simply use  kubectl get services -n  lt namespace-name gt   this will help you

User · Answer

You can achieve this by deploying something at a higher layer than namespaced Services  like the service loadbalancer  https   github com kubernetes contrib tree master service-loadbalancer  If you want to restrict it to a single namespace  use  --namespace ns  argument  it defaults to all namespaces  https   github com kubernetes contrib blob master service-loadbalancer service loadbalancer go L715   This works well for L7  but is a little messy for L4

User · Answer

I stumbled over the same issue and found a nice solution which does not need any static ip configuration   You can access a service via it s DNS name  as mentioned by you   servicename namespace svc cluster local  You can use that DNS name to reference it in another namespace via a local service   kind  Service apiVersion  v1 metadata    name  service-y   namespace  namespace-a spec    type  ExternalName   externalName  service-x namespace-b svc cluster local   ports    - port  80

[kubernetes] Service located in another namespace

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