I am running a mariadb instance in a docker container. It is connected to a custom bridge network. Let's call it db_net here.
Now I want to connect to mariadb from another container connected to the same network.
I can ping the mariadb container from the other container with ping mariadb.db_net. It resolves to some 172.x.x.x IP.
Setting up the grant table in mariadb with numeric IPs works. But obviously these may change in a modified setup. I also would like to avoid using all wildcards (e.g 172.%.%.%) since other containers may also use the same mariadb instance.
Using the symbolic host name (name.db_net) in the grants table fails.
What is the recommended way to solve this? Using all wildcards in the host field and relying on other isolation mechanisms of course works, but it seems like doing that I give up a layer of security that would be desirable.
Sometimes embedded DNS doesn’t work fine with Linux services. The best approach is DNS to resolve hostnames to IP addresses. It can be by modifying /etc/hosts file or using a third party DNS server. This will ensure that whenever the IP address changes, database privileges still works fine.
If you choose to setup DNS server in your docker network, each container will have to be started with the option.
--dns=IP_ADDRESS
The address provided will then be written to the file /etc/resolv.conf on the docker container.
Related
I am building a microservices based application and would like to use Consul as service registry. All in all I have three scenarios:
All the services run on the host.
All the services run on the host, but Consul runs in Docker.
All the services and Consul run in Docker.
Now I have the problem of how to register the services with their IP address, because I need to figure out their IP address so that it is reachable by Consul (e.g., for the health checks):
If everything runs on the same host, it's pretty easy: Simply use 127.0.0.1, and you're done.
If everything (including Consul) runs in Docker, I could use hostname -i from within the Docker containers to figure out their external IP and hand it over to Consul. This works, but I wonder if there is a better way to solve this? (Ideally, the solution should also work in the same way on Kubernetes.)
If the services run on the host, but Consul runs in Docker, right now I am missing any idea at all. Basically, Consul requires the host's IP address to be able to talk to the services, but I can only detect this from within the Consul container (by resolving host.docker.internal). But first, this does not work from externally, and second it only works for Docker for Mac / Windows, not e.g. with Kubernetes.
How could I solve these issues?
PS: I would like to avoid using a container such as registrator by Gliderlabs, since I have doubts how well this works on Kubernetes, and also it won't help with the mixed Docker / host scenario.
If you're using Kubernetes, you might start by checking whether its built-in service registry meets your needs. There's generally not a direct path to reach a pod via its node's host's IP address, so the setup you describe won't really work well. (I might consider Consul for a key/value store but I wouldn't reach for it as a service registry in Kubernetes land.)
In plain multi-host Docker land, this is one of the few situations I've found where host networking is appropriate. Start Consul with --net host or an equivalent option in Docker Compose or another orchestration tool. Then Consul will believe "its" IP address is the host's, and if you have automated TCP probes of well-known ports, you can search every service that's running on the host and discover e.g. a MySQL service on port 3306, whether running in a container or natively on the host.
With this setup, servicename.service.consul will resolve to some physical-host IP address. If you have a Docker container pointing at its current host for DNS service, then that will route a service to some host, maybe the same one, but this has worked reliably for me in the past.
Note that the relevant hostnames will be different in different environments: servicename.service.consul for a Consul-based setup, servicename.namespacename.svc.cluster.local in Kubernetes, maybe localhost in a developer-desktop environment. You need to make sure this is configurable, most straightforwardly via an environment variable.
I've had db and server container, both running in the same network. Can ping db host by its container id with no problem.
When I set a hostname for db container manually (-h myname), it had an effect ($ hostname returns set host), but I can't ping that hostname from another container in the same network. Container id still pingable.
Although it works with no problem in docker compose.
What am I missing?
Hostname is not used by docker's built in DNS service. It's a counterintuitive exception, but since hostnames can change outside of docker's control, it makes some sense. Docker's DNS will resolve:
the container id
container name
any network aliases you define for the container on that network
The easiest of these options is the last one which is automatically configured when running containers with a compose file. The service name itself is a network alias. This lets you scale and perform rolling updates without reconfiguring other containers.
You need to be on a user created network, not something like the default bridge which has DNS disabled. This is done by default when running containers with a compose file.
Avoid using links since they are deprecated. And I'd only recommend adding host entries for external static hosts that are not in any DNS, for container to container, or access to other hosts outside of docker, DNS is preferred.
I've found out, that problem can be solved without network using --add-host option. Container's IP can be gain using inspect command.
But when containers in the same network, they are able to access each other via it names.
As stated in the docker docs, if you start containers on the default bridge network, adding -h myname will add this information to
/etc/hosts
/etc/resolv.conf
and the bash prompt
of the container just started.
However, this will not have any effect to other independent containers. (You could use --link to add this information to /etc/hosts of other containers. However, --link is deprecated.)
On the other hand, when you create a user-defined bridge network, docker provides an embedded DNS server to make name lookups between containers on that network possible, see Embedded DNS server in user-defined networks. Name resolution takes the container names defined with --name. (You
will not find another container by using its --hostname value.)
The reason, why it works with docker-compose is, that docker-compose creates a custom network for you and automatically names the containers.
The situation seems to be a bit different, when you don't specify a name for the container yourself. The run reference says
If you do not assign a container name with the --name option, then the daemon generates a random string name for you. [...] If you specify a name, you can use it when referencing the container within a Docker network.
In agreement with your findings, this should be read as: If you don't specify a custom --name, you cannot use the auto-generated name to look up other containers on the same network.
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'm trying to make a docker machine available to my Windows by a host name. After creating it like
docker-machine create -d virtualbox mymachine
and setting up a docker container that exposes the port 80, how can I give that docker machine a host name such that I can enter "http://mymachine/" into my browser to load the website? When I change "mymachine" to the actual IP address then it works.
There is an answer to this question but I would like to achieve it without an entry in the hosts file. Is that possible?
You might want to refer to docker documentaion:
https://docs.docker.com/engine/userguide/networking/#exposing-and-publishing-ports
You expose ports using the EXPOSE keyword in the Dockerfile or the
--expose flag to docker run. Exposing ports is a way of documenting which ports are used, but does not actually map or open any ports.
Exposing ports is optional.
You publish ports using the --publish or --publish-all flag to docker
run. This tells Docker which ports to open on the container’s network
interface. When a port is published, it is mapped to an available
high-order port (higher than 30000) on the host machine, unless you
specify the port to map to on the host machine at runtime. You cannot
specify the port to map to on the host machine when you build the
image (in the Dockerfile), because there is no way to guarantee that
the port will be available on the host machine where you run the
image.
I also suggest reviewing the -P flag as it differs from the -p one.
Also i suggest you try "Kitematic" for Windows or Mac, https://kitematic.com/ . It's much simpler (but dont forget to commit after any changes!)
Now concerning the network in your company, it has nothing to do with docker, as long as you're using docker locally on your computer it wont matter what configuration your company set. Even you dont have to change any VM network config in order to expose things to your local host, all comes by default if you're using Vbox ( adapter 1 ==> NAT & adapter 2 ==> host only )
hope this is what you're looking for
If the goal is to keep it as simple as possible for multiple developers, localhost will be your best bet. As long as the ports you're exposing and publishing are available on host, you can just use http://localhost in the browser. If it's a port other than 80/443, just append it like http://localhost:8080.
If you really don't want to go the /etc/hosts or localhost route, you could also purchase a domain and have it route to 127.0.0.1. This article lays out the details a little bit more.
Example:
dave-mbp:~ dave$ traceroute yoogle.com
traceroute to yoogle.com (127.0.0.1), 64 hops max, 52 byte packets
1 localhost (127.0.0.1) 0.742 ms 0.056 ms 0.046 ms
Alternatively, if you don't want to purchase your own domain and all developers are on the same network and you are able to control DHCP/DNS, you can setup your own DNS server to include a private route back to 127.0.0.1. Similar concept to the Public DNS option, but a little more brittle since you might allow your devs to work remote, outside of a controlled network.
Connecting by hostname requires that you go through hostname to IP resolution. That's handled by the hosts file and falls back to DNS. This all happens before you ever touch the docker container, and docker machine itself does not have any external hooks to go out and configure your hosts file or DNS servers.
With newer versions of Docker on windows, you run containers with HyperV and networking automatically maps ports to localhost so you can connect to http://localhost. This won't work with docker-machine since it's spinning up virtualbox VM's without the localhost mapping.
If you don't want to configure your hosts file, DNS, and can't use a newer version of docker, you're left with connecting by IP. What you can do is use a free wildcard DNS service like http://xip.io/ that maps any name you want, along with your IP address, back to that same IP address. This lets you use things like a hostname based reverse proxy to connect to multiple containers inside of docker behind the same port.
One last option is to run your docker host VM with a static IP. Docker-machine doesn't support this directly yet, so you can either rely on luck to keep the same IP from a given range, or use another tool like Vagrant to spin up the docker host VM with a static IP on the laptop. Once you have a static IP, you can modify the host file once, create a DNS entry for every dev, or use the same xip.io URL, to access the containers each time.
If you're on a machine with Multicasting DNS (that's Bonjour on a Mac), then the approach that's worked for me is to fire up an Avahi container in the Docker Machine vbox. This lets me refer to VM services at <docker-machine-vm-name>.local. No editing /etc/hosts, no crazy networking settings.
I use different Virtualbox VMs for different projects for my work, which keeps a nice separation of concerns (prevents port collisions, lets me blow away all the containers and images without affecting my other projects, etc.)
Using docker-compose, I just put an Avahi instance at the top of each project:
version: '2'
services:
avahi:
image: 'enernoclabs/avahi:latest'
network_mode: 'host'
Then if I run a webserver in the VM with a docker container forwarding to port 80, it's just http://machine-name.local in the browser.
You can add a domain name entry in your hosts file :
X.X.X.X mymachine # Replace X.X.X.X by the IP of your docker machine
You could also set up a DNS server on your local network if your app is meant to be reachable from your coworkers at your workplace and if your windows machine is meant to remain up as a server.
that would require to make your VM accessible from local network though, but port forwarding could then be a simple solution if your app is the only webservice running on your windows host. (Note that you could as well set up a linux server to avoid using docker-machine on windows, but you would still have to set up a static IP for this server to ensure that your domain name resolution works).
You could also buy your own domain name (or get a free one) and assign it your docker-machine's IP if you don't have rights to write in your hosts file.
But these solution may not work anymore after some time if app host doesn't have a static IP and if your docker-machine IP changes). Not setting up a static IP doesn't imply it will automatically change though, there should be some persistence if you don't erase the machine to create a new one, but that wouldn't be guaranteed either.
Also note that if you set up a DNS server, you'd have to host it on a device with a static IP as well. Your coworkers would then have to configure their machine to use this one.
I suggest nginx-proxy. This is what I use all the time. It comes in especially handy when you are running different containers that are all supposed to answer to the same port (e.g. multiple web-services).
nginx-proxy runs seperately from your service and listens to docker-events to update it's own configuration. After you spun up your service and query the port nginx-proxy is listening to, you will be redirected to your service. Therefore you either need to start nginx-proxy with the DEFAULT_HOST flag or send the desired host as header param with the request.
As I am running this only with plain docker, I don't know if it works with docker-machine, though.
If you go for this option, you can decide for a certain domain (e.g. .docker) to be completely resolved to localhost. This can be either done company-wide by DNS, locally with hosts file or an intermediate resolver (the specific solution depends on your OS, of course). If you then try to reach http://service1.docker nginx-proxy will route to the container that has then ENV VIRTUAL_HOST=service1.docker. This is really convenient, because it only needs one-time setup and is from then on dynamic.
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/