I want to create two Docker 1.9 networks. Network A runs a web server, an application server, and a Postgres server (all containers). Network B runs a SMTP server and other containers. I need containers on Network A to get to Network B. Is it possible?
The libnetwork implementation includes an overlay mode:
The overlay driver implements networking that can span multiple hosts using overlay network encapsulations such as VXLAN. For more details on its design, please see the Overlay Driver Design.
The new native overlay network driver supports multi-host networking natively out-of-the-box.
This support is accomplished with the help of libnetwork, a built-in VXLAN-based overlay network driver, and Docker's libkv library.
This tutorial explains how to make containers talk to each other even if they are on different machines, provided they are registered to the same overlay network.
That will involve setting up first a K/V (Key/Value) store:
Now that your three nodes are configured to use the key-value store, you can create an overlay network on any node. When you create the network, it is distributed to all the nodes.
When you create your first overlay network on any host, Docker also creates another network on each host called docker_gwbridge. Docker uses this network to provide external access for containers.
Every container in an overlay network also gets an eth interface in the docker_gwbridge which allows the container to access the external world.
The docker_gwbridge is similar to Docker's default bridge network, but unlike the bridge it restricts Inter-Container Communication(ICC).
Docker creates only one docker_gwbridge bridge network per host regardless of the number of overlay networks present.
Docker added an entry to /etc/hosts for each container that belongs to the RED overlay network.
Therefore, to reach container2 from container1, you can simply use its name. Docker automatically updates /etc/hosts when containers connect and disconnect from an overlay network.
At this point, container2 and container3 can communicate over the RED overlay network.
They are both on the same docker_gwbridge but they cannot communicate using that bridge network without host-port mapping. The docker_gwbridge is used for all other traffic.
Related
I am new to Dockers and containers. I was going through the tutorials for docker and came across this information.
https://docs.docker.com/get-started/part3/#docker-composeyml
networks:
- webnet
networks:
webnet:
What is webnet? The document says
Instruct web’s containers to share port 80 via a load-balanced network called webnet. (Internally, the containers themselves will publish to web’s port 80 at an ephemeral port.)
So, by default, the overlay network is load balanced in docker cluster? What is load balancing algo used?
Actually, it is not clear to me why do we have load balancing on the overlay network.
Not sure I can be clearer than the docs, but maybe rephrasing will help.
First, the doc you're following here uses what is called the swarm mode of docker.
What is swarm mode?
A swarm is a cluster of Docker engines, or nodes, where you deploy services. The Docker Engine CLI and API include commands to manage swarm nodes (e.g., add or remove nodes), and deploy and orchestrate services across the swarm.
From SO Documentation:
A swarm is a number of Docker Engines (or nodes) that deploy services collectively. Swarm is used to distribute processing across many physical, virtual or cloud machines.
So, with swarm mode you have a multi host (vms and/or physical) cluster a machines that communicate with each other through their docker engine.
Q1. What is webnet?
webnet is the name of an overlay network that is created when your stack is launched.
Overlay networks manage communications among the Docker daemons participating in the swarm
In your cluster of machines, a virtual network is the created, where each service has an ip - mapped to an internal DNS entry (which is service name), and allowing docker to route incoming packets to the right container, everywhere in the swarm (cluster).
Q2. So, by default, overlay network is load balanced in docker cluster ?
Yes, if you use the overlay network, but you could also remove the service networks configuration to bypass that. Then you would have to publish the port of the service you want to expose.
Q3. What is load balancing algo used ?
From this SO question answered by swarm master bmitch ;):
The algorithm is currently round-robin and I've seen no indication that it's pluginable yet. A higher level load balancer would allow swarm nodes to be taken down for maintenance, but any sticky sessions or other routing features will be undone by the round-robin algorithm in swarm mode.
Q4. Actually it is not clear to me why do we have load balancing on overlay network
Purpose of docker swarm mode / services is to allow orchestration of replicated services, meaning that we can scale up / down containers deployed in the swarm.
From the docs again:
Swarm mode has an internal DNS component that automatically assigns each service in the swarm a DNS entry. The swarm manager uses internal load balancing to distribute requests among services within the cluster based upon the DNS name of the service.
So you can have deployed like 10 exact same container (let's say nginx with you app html/js), without dealing with private network DNS entries, port configuration, etc... Any incoming request will be automatically load balanced to hosts participating in the swarm.
Hope this helps!
When using Docker swarm mode and exposing ports outside, you have at least three networks, the ingress network, the bridge network and the overlay network (used for internal cluster communications). The container joins these networks using one of eth0-2 (randomically each time) interfaces and from an application point of view is not easy to understand which of these is the cluster network (the correct one to use for service discovery client publish - e.g Spring Eureka).
Is there a way to customize network interface names in some way?
Not a direct answer to your question, but one of the key selling points of swarm mode is the built-in service discovery mechanism, which in my opinion works really nicely.
More related, I don't think it's possible to specify the desired interface for an overlay network. However, when creating a network, it is possible to define the subnet or the IP range of the network (https://docs.docker.com/engine/reference/commandline/network_create/). You could use that to identify the interface belonging to your overlay network, by checking if the bound IP address is part of the network you want to publish on.
Let's say I have two docker networks on the same machine. (Network-1 and Network-2)
On each network, I have containers. (Container-1-Network-1 and Container-1-Network-2 etc.)
I need to send a PUT request from Container-1(172.18.0.x) to Container-2 (172.19.0.x) but I get 'connection refused' because different networks can't communicate with each other. What are my options here? Can I move a container to another network, or merge networks into one or link containers somehow (in docker-compose.yml)?
Thanks.
Ideally, you should add the container to every network where it needs to communicate with other containers and each network should be isolated from each other. This is the default design of docker networking.
To add containers to another network, use:
docker network connect $network $container
An easier method when you have lots of containers to manage is to use docker compose to define which networks each container needs to belong to. This automates the docker network connect commands.
I'm using Docker to network together two containers and one of the containers needs to be able to access the host network for service discovery. I cannot use -net=host because that makes the other container inaccessible.
What I am looking for is essentially a way to add the host network as a "secondary" network to the docker container so it can access other containers, as well as the host network.
Hopefully that makes sense. Docker is still very new to me so I apologize if my explanation is lacking.
EDIT: To elaborate more on the kind of discovery I need, basically I am running Plex media server inside a container and PlexConnect inside another container. In order for PlexConnect to be able to detect the right IP for Plex, it needs to be able to access the 192.168 local network of the host since it serves as the DNS for an AppleTV outside the Docker network.
So containers are as follows:
Plex (bridge mode and binds to the host port 192.168.1.100:32400)
PlexConnect (separate subnet of bridge mode, needs to be able to access 192.168.1.100:32400)
tl;dr I need what BMitch suggested below but the docker-compose version.
With new network feature in docker 1.10 it is possible to create isolated overlay networks - which works very well. Containers in 2 separate networks can not talk to each other. Is it possible, however, to deny container in overlay network to reach public internet? Eg to make ping 8.8.8.8 fail, while having docker host connected to internet.
If you add the --internal flag when creating a network with the docker network create command, then that network will not have outbound network access:
docker network create --internal --subnet 10.1.1.0/24 mynetwork
I assume -- but have not tested -- that this works for overlay networks as well as for host-local networks.