I'm working locally (within Docker for Mac) on a Kubernetes cluster that will eventually be deployed to the cloud. We plan to use a database service in that environment. To simulate that, I'd like to have the services in the cluster connect to a database running outside the cluster on my laptop.
Can I do that? Here's what I thought I'd try.
Service with type: ExternalName and externalName: somedb.local127.0.0.1 somedb.local to /etc/hosts on the laptopIs that correct? Is there a better way?
After talking with some colleagues, I found a solution.
In Docker for Mac, host.docker.internal points to the host machine, and that lets me connect to the db running there, even from containers running in the K8s cluster.
You may have a Service pointing to an address out of your SDN, by creating an Endpoint object with matching name.
----
apiVersion: v1
kind: Service
metadata:
name: external-db
namespace: my-namespace
spec:
ports:
- name: exporter-3306
port: 3306
selector:
name: external-db
---
apiVersion: v1
kind: Endpoints
metadata:
name: external-db
namespace: my-namespace
subsets:
- addresses:
- ip: 10.42.253.110
ports:
- name: exporter-3306
port: 3306
You may add hosts overrides in your Deployment definition:
apiVersion: apps/v1
kind: Deployment
spec:
template:
spec:
containers:
...
hostAliases:
- ip: 10.42.253.110
hostnames:
- external-db
It seems the Kubernetes docs provide an instruction on how to achieve this. https://kubernetes.io/docs/concepts/services-networking/service/#services-without-selectors
A note says endpoint IPs must not be: loopback (127.0.0.0/8 for IPv4, ::1/128 for IPv6), or link-local (169.254.0.0/16 and 224.0.0.0/24 for IPv4, fe80::/64 for IPv6).