With k3d, I am receiving a DNS error when the pod tries to access a URL over the internet.
ERROR:
getaddrinfo EAI_AGAIN DNS could not be resolved
How can I get past this error?
It depends on your context, OS, version.
For instance, you will see various proxy issue in k3d-io/k3d issue 209
this could be related to the way k3d creates the docker network.
Indeed, k3d creates a custom docker network for each cluster and when this happens resolving is done through the docker daemon.
The requests are actually forwarded to the DNS servers configured in your host's resolv.conf. But through a single DNS server (the embedded one of docker).
This means that if your daemon.json is, like mine, not configured to provide extra DNS servers it defaults to 8.8.8.8 which does not resolve any company address for example.
It would be useful to have a custom options to provide to k3d when it starts the cluster and specify the DNS servers there
Which is why there is "v3/networking: --network flag to attach to existing networks", referring to Networking.
Before that new flag:
For those who have the problem, a simple fix is to mount your /etc/resolve.conf onto the cluster:
k3d cluster create --volume /etc/resolv.conf:/etc/resolv.conf
Related
I'm trying to start minikube on ubuntu 18.04 inside nginx proxy manager docker network in order to setup some kubernetes services and manage the domain names and the proxy hosts in the nginx proxy manager platform.
so I have nginxproxymanager_default docker network and when I run minikube start --network=nginxproxymanager_default I get
Exiting due to GUEST_PROVISION: Failed to start host: can't create with that IP, address already in use
what might I been doing wrong?
A similar error was reported with kubernetes/minikube issue 12894
please check whether there are other services using that IP address, and try starting minikube again.
Considering minikube start man page
--network string
network to run minikube with.
Now it is used by docker/podman and KVM drivers.
If left empty, minikube will create a new network.
Using an existing NGiNX network (as opposed to docker/podman) might not be supported.
I have seen NGiNX set up as ingress, not directly as "network".
I am currently developing docker containers using visual studio, and these container images are supposed to run in a kubernetes cluster that I am also running locally.
Currently, the docker container that is running via visual studio is not being deployed to a kubernetes cluster, but for some reason am I able to ping the kubernetes pod's ip address from the docker container, but for which I don't quite understand; should they not be separated, and not be able to reach each other?
And it cannot be located on the kubernetes dashboard?
And since they are connected, why can't I use the kubernetes service to connect to my pod from my docker container?
The docker container is capable of pinging the cluster IP, meaning that it is reachable.
nslookup the service is not able to resolve the hostname.
So, as I already stated in the comment:
When Docker is installed, a default bridge network named docker0 is
created. Each new Docker container is automatically attached to this
network, unless a custom network is specified.
Thats mean you are able to ping containers by their respective IP. But you are not able to resolve DNS names of cluster objects - you VM know nothing about internal cluster DNS server.
Few option what you can do:
1) explicitly add record of cluster DNS to /etc/hosts inside VM
2) add a record to /etc/resolv.conf with nameserver and search inside VM. See one of my answers related to DNS resolution on stack: nslookup does not resolve Kubernetes.default
3)use dnsmasq as described in Configuring your Linux host to resolve a local Kubernetes cluster’s service URLs article. Btw I highly recommend you read it from the beginning till the end. It greatly describes how to work with DNS and what workaround you can use.
Hope it helps.
I have a spring boot service which runs fine as spring boot app. I have created docker image out of it using docker file. When the image start, application seems starting fine till a point when it try to resolve external host (I have couple fo external service configured based on profile and I am running in dev profile which will communicate with external service like consule , mysql etc). It throws unknownhost exception. Same application run fine and able to run and communicate with external services while running it as spring boot app/service in my local machine . It seems like the issue is between host and docker container not able to use dns of host. Any help, how can I resolve the issue ?
From the Docker documentation:
https://docs.docker.com/config/containers/container-networking/#ip-address-and-hostname
DNS services
By default, a container inherits the DNS settings of the Docker
daemon, including the /etc/hosts and /etc/resolv.conf.You can override
these settings on a per-container basis.
Flag Description
--dns The IP address of a DNS server. To specify multiple DNS servers, use
multiple --dns flags. If the container cannot reach any of the IP
addresses you specify, Google’s public DNS server 8.8.8.8 is added,
so that your container can resolve internet domains.
--dns-search A DNS search domain to search non-fully-qualified hostnames.
To specify multiple DNS search prefixes, use multiple --dns-search flags.
--dns-opt A key-value pair representing a DNS option and its value. See your
operating system’s documentation for resolv.conf for valid options.
--hostname The hostname a container uses for itself. Defaults to the container’s
ID if not specified.
See also:
Docker docs: Configure container DNS
java.net.UnknownHostException on Docker
How do you access remote Docker container by its hostname?
I need to access remote Docker containers by its hostnames (or some constant IP's) for development and testing purposes. I have tried:
looking for any DNS approach (have not found any clues),
importing /ets/hosts (probably impossible),
creating tunnes (only this works but it is very time consuming).
It's the same as running any other process on a host, Docker or not Docker: you access it via the host name or IP address of the host and the port the service is listening on (the first port of the docker run -p argument). Docker containers don't have externally visible individual IP addresses any more than non-Docker HTTP or ssh daemons do.
If you do have DNS infrastructure available to you, you could set up CNAME records to resolve particular service names to the specific hosts that are running them.
One solution that may help you is some sort of service registry; in the past I've used Consul with some success. You can configure Consul with some health checks or other probes ("look for an HTTP service on port 12345 that answers GET / calls"), and it will provide its own DNS service ("okay, http://whatevername.service.consul:12345/ will reach your service on whichever hosts it happens to be running on").
Nothing in the Docker infrastructure specifically helps this. Using /etc/hosts is distinctly not a best practice: the name-to-IP mapping needs to be kept in sync across all machines and you'll start wishing you had a network service to publish it for you, which is exactly what DNS is for.
I have a docker container that needs to access an network server on the LAN. This server is visible from the docker host machine and I can access it from within the container when I reference the IP address directly.
However I need to be able to specify a url and port (e.g http://myserver:8080) rather than an IP address, which the docker container cannot resolve.
How can I configure the container to resolve this? ideally using the docker hosts dns. I have looked at many of the docs, but not being a DNS expert, it doesn't seem straightforward.
UPDATE:
I have tried this, which seems to work, but does this have any downsides or unintended consequences?
--network host
Thanks,
The rigth way to do this is to configure the docker daemon dns as specified under daemon-dns-options.
Using the host network is not recommended as it has some downsides https://docs.docker.com/network/host/