I want to connect a docker container running locally to a service running on a Kubernetes cluster. To do so I have exposed a service through reserving some static IP addresses.
I have also saved those IP addresses in local DNS, in the /etc/hosts/ file:
123.123.123.12 host1
456.456.456.45 host2
I want to link my container to that such that all the traffic is routed to those addresses so that it can be processed by the cluster. I am using the link feature in the docker container but it isn't working.
I want to connect directly using IP? How should I do this?
There's no difference doing this if the client is or isn't in Docker. However you have the service exposed from Kubernetes, you'd make the same connection to it from a process running on an external host or from a process running in a Docker container on that host.
Say, as in the example in the Kubernetes documentation, you're running a NodePort service that's accessible on port 31496 on every node in the cluster, and you're trying to connect to it from outside the cluster. Maybe as in the question 123.123.123.12 is some node in the cluster. A typical setup would be to get the location of the service from an environment variable (JavaScript process.env.THE_SERVICE_URL; Ruby ENV['THE_SERVICE_URL']; Python os.environ['THE_SERVICE_URL']; ...).
When you're developing, you could set that variable in your local shell:
export THE_SERVICE_URL=http://123.123.123.12:31496
cd here && ./kubernetes_client_script.py
When you go to deploy your application, you can set the same environment variable:
docker run -e THE_SERVICE_URL=http://123.123.123.12:31496 me:k8s-client
Related
Here's a scenario:
Host (local computer running macOS) has access to the number of services running on various IPs within the 127.1.1.0/24 network range.
That network is not a real local network, but instead done through kubectl port-forward (and maybe some other magic xD). That basically gives host access to the services running in the remote K8s cluster namespace. For context, that is achieved through Bridge to Kubernetes VSCode extension.
Host can ping or curl any of those services via their respective IPs and ports on the 127.1.1.0/24 network. E.g. curl 127.1.1.15:9098
How to make a service running inside the docker container on the host (local machine) be able to send network requests to any of those port-forwarded remote services with 127.1.1.0/24 IPs?
Any potential solutions appreciated. Thanks.
I have a running k3d Kubernetes cluster:
$ kubectl cluster-info
Kubernetes master is running at https://0.0.0.0:6550
CoreDNS is running at https://0.0.0.0:6550/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
Metrics-server is running at https://0.0.0.0:6550/api/v1/namespaces/kube-system/services/https:metrics-server:/proxy
I have a python script that uses the kubernetes client api and manages namespaces, deployments, pod, etc. This works just fine in my local environment because I have all the necessary python modules installed and have direct access to my local k8s cluster. My goal is to containerize so that this same script is successfully run for my colleagues on their systems.
While running the same python script in a docker container, I receive connection errors:
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='172.17.0.1', port=6550): Max retries exceeded with url: /api/v1/namespaces (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7f8b637c5d68>: Failed to establish a new connection: [Errno 113] No route to host',))
172.17.0.1 is my docker0 bridge address so assumed that would resolve or forward traffic to my localhost. I have tried loading k8s configuration from my local .kube/config which references server: https://0.0.0.0:6550 and also creating a separate config file with server: https://172.17.0.1:6550 and both give the same No route to host error (with the respective ip address in the HTTPSConnectionPool(host=...))
One idea I was pursing was running a socat process outside the container and tunnel traffic from inside the container across a bridge socket mounted in from the outside, but looks like the docker image I need to use does not have socat installed. However, I get the feeling like the real solution should be much simplier than all of this.
Certainly there have been other instances of a docker container needing access to a k8s cluster served outside of the docker network. How is this connection typically established?
Use docker network command to create a predefined network
You can pass --network to attach k3d to an existing Docker network and also to docker run to do the same for another container
https://k3d.io/internals/networking/
I'm using a Digital Ocean docker droplet and have 3 docker containers: 1 for front-end, 1 for back-end and 1 for other tools with different dependencies, let's call it back-end 2.
The front-end calls the back-end 1, the back-end 1 in turn calls the back-end 2. The back-end 2 container exposes a gRPC service over port 50051. Locally, by running the following command, I was able to identify the docker service to be running with the IP 127.17.0.1:
docker network inspect bridge --format='{{json .IPAM.Config}}'
Therefore, I understand that my gRPC server is accessible from the following url 127.17.0.1:50051 within the server.
Unfortunately, the gRPC server refuses connections when running from the docker droplet while it works perfectly well when running locally.
Any idea what may be different?
You should generally set up a Docker private network to communicate between containers using their container names; see e.g. How to communicate between Docker containers via "hostname". The Docker-internal IP addresses are subject to change if you delete and recreate a container and aren't reachable from off-host, and trying to find them generally isn't a best practice.
172.17.0.0/16 is a typical default for the Docker-internal IP network (127.0.0.0/8 is the reserved IPv4 loopback network) and it looks like you might have typoed the address you got from docker network inspect.
Try docker run with following command:
docker run -d -p {server ip}:12345 {back-end 2 image}
It will expose IP port to docker container and will be accessible from other servers.
Note: also check firewall rules, if firewall is blocking access.
You could run docker binding to ip and port as shown by Aakash. Please restrict access to this specific IP and port to be accessed only from the other docker IP and port - this will help to run docker private and doesn't allow other (even the other docker/instances within your network).
What I want to do is run kubernetes within docker and expose the kubernetes services externally. I followed the docs on getting kubernetes running within docker. As long as I connect from the localhost, I can access my services. However, connecting from a different computer doesn't work. If I spin up a docker image directly, then I can access it. Only things running within kubernetes aren't exposed. Is this possible?
Ensure your nodes have externally reachable IP addresses.
Then create a service of type NodePort:
https://github.com/kubernetes/kubernetes/blob/master/docs/user-guide/services.md#type-nodeport
And direct traffic to nodes at the allocated port.
An application server is running as one Docker container and database running in another container. IP address of the database server is obtained as:
sudo docker inspect -f '{{ .NetworkSettings.IPAddress }}' db
Setting up JDBC resource in the application server to point to the database gives "java.net.ConnectException".
Linking containers is not an option since that only works on the same host.
How do I ensure that IP address of the database container is visible to the application server container?
If you want private networking between docker containers on remote hosts you can use weave to setup an overlay network between docker containers. If you don't need a private network just expose the ports using the -p switch and configure the addresses of the host machine as the destination IP in the required docker container.
One simple way to solve this would be using Weave. It allows you to create many application-specific networks that can span multiple hosts as well as datacenters. It also has a very neat DNS-based service discovery mechanism.
I should disclaim, I am one of Weave engineering team.
Linking containers is not an option since that only works on the same host.
So are you saying your application is a container running on docker server 1 and your db is a container on docker server 2? If so, you treat it like ordinary remote hosts. Your DB port needs to be exposed on docker server 2 and that IP:port needs to be configured into your application server, typically via environment variables.
The per host docker subnetwork is a Private Network. It's perhaps possible to have this address be routable, but it would be much pain. And it's further complicated because container IP's are not static.
What you need to do is publish the ports/services up to the host (via PORT in dockerfile and -p in your docker run) Then you just do host->host. You can resolve hosts by IP, Environment Variables, or good old DNS.
Few things were missing that were not allowing the cross-container communication:
WildFly was not bound to 0.0.0.0 and thus was only accepting requests on eht0. This was fixed using "-b 0.0.0.0".
Firewall was not allowing the containers to communication. This was removed using "systemctl stop firewall; systemctl disable firewall"
Virtual Box image required a Host-only adapter
After this, the containers are able to communicate. Complete details are available at:
http://blog.arungupta.me/2014/12/wildfly-javaee7-mysql-link-two-docker-container-techtip65/