I've currently got two fairly vanilla CentOS 7 boxes that are running under a Docker Swarm, one a master and the other joined to it. In that swarm, I want to have a stack running that will essentially be my Plex / multimedia system. I've got the docker_compose.yml file for that linked. I can deploy the file to the swarm using the following command:
docker stack deploy --compose-file docker-compose.yml plexsystem
That works fine, it deploys the containers like you would expect. The issue I'm having is that the containers do not have external internet access, so if the container needs to download any files or interact with APIs, they fail. I interact with containers with docker exec -it container /bin/bash and try to ping out, and it always fails.
What do I need to add or change to my docker-compose.yml file so that my networking can work and I can finally get my stack working as it should. I've been banging my head with this one and I cannot figure out how to get swarm networking. Thank you very much!
Checkout your docker daemon file and look for the iptables parameter configuration. Most probably it is set to false and hence it is not able to access the internet.
--iptables=false prevents the Docker daemon from adding iptables rules. If multiple daemons manage iptables rules, they may overwrite rules set by another daemon. Be aware that disabling this option requires you to manually add iptables rules to expose container ports. If you prevent Docker from adding iptables rules, Docker will also not add IP masquerading rules, even if you set --ip-masq to true. Without IP masquerading rules, Docker containers will not be able to connect to external hosts or the internet when using network other than default bridge.
Related
I am quite new to the docker topics and I have a question of connecting container services with traditional ones.
Currently I am thinking of replacing an traditional grafana installation (directly on a linux server) with a grafana docker container.
In grafana I have to connect to different data sources like a mysql instance, a Winsows SQL Database and so on. So grafana is doing a pull of data. All these data sources reside (and will still reside) on other hosts and they are not containers.
So how can I implement that my container is able to communicate with this data sources? Is it possible by default or do I have to implement a special kind of network? I saw that there is an option called macvlan...is that the correct way?
BR
Jan
This should work out of the box, as far as I understand. At least, I'm using Grafana inside a docker container and it works perfectly.
You can test a connectivity from inside your docker container to some external resource by opening a container shell like this:
docker exec -it <container ID> /bin/bash
And then
root#a9cbebfc4564:/# curl google.com
Or
root#a9cbebfc4564:/# ping <bla-bla>
Commands above depend on a docker image environment (like OS or installed software), but this can be solved in a same was as you can do on a regular Unix env
P.S. I encountered a docker2host connection issue once, but it was due to incorrect firewall configuration on a host side.
Since you are replacing a traditional installation, you can start with host networking. This mode give you same connectivity experience as installing on the host. A quick start is as simple as:
docker run --network host grafana/grafana
Notice there's no need to --publish or --publish-all ports as the Grafana container now share the host network.
Say we provision an overlay network using docker swarm and create various containers with following names:
Alice
Bob
Larry
John
now if we try to ping any container from another it fails because it does not know how to do the IP lookup i.e., alice does not know bob's IP and so on. We have been taking care of this by manually editing the /etc/hosts on every container and entering the name/IP key value pair in that file but this is becoming very tedious with every restart of our network. There ought to be a better way of handling this.
E.g., services created using docker stack do not suffer from this problem. Due to various reasons we are stuck with creating containers using the vanilla docker create. How can we make containers discover each other on the overlay network without manual labor of editing /etc/hosts?
Below is detailed workflow we currently have to follow:
we first provision a docker swarm and overlay network
Then for each container, we create it using the docker create command and then start it using docker start command. we use the --network flag to attach the container to the overlay network at time of creation
We then use docker container inspect to get the IP address of each container. This involves running n commands and noting down IP address.
Then we log into each container and edit the /etc/hosts file by hand and enter the (name, IP) key-value pair of the other containers. So this means having to enter n*(n-1) records by hand when summed across containers.
Not sure why docker create does not do all this automatically - docker already knows (or can know) all the IP addresses. Containers provisioned using docker stack e.g., do not have to go through this manual process to "discover" each other. The reason why we cannot use docker stack is because:
it does not allow us to specify container name
we run various commands (mostly docker cp) before starting the container and not possible to do this using stack
You might have seen this already: DNS on User defines networks
Have you created your services like in the section „Attach a service to an overlay“ in this doc?
It seems that the only thing that is needed is to refer the containers by their {name}.{network} instead of just the {name}. No need to edit /etc/hosts or use the --add-host flag or run some additional dns server. Refer https://forums.docker.com/t/need-help-connecting-containers-in-swarm-mode/77944/6
Further details: the official documentation for docker does not mention anywhere the necessity to add .{network} suffix to the {containername}. Indeed on this link, Step #7 under the Walk-through, there is no .{network} suffix used. So not sure why we need to do that. The version of docker we are using is 18.06.1-ce for linux.
I had a similar issue : I'm following this official tutorial to create a docker swarm overlay network on two Raspberry pi 3 and the ping was impossible unless I found on Github the answer : as I understood, it seems that latest version of alpine (for a reason that I ignore) is not suitable for Raspberry pi 3 so the solution would be the use of the version 3.12.3 like this : sudo docker run -dit --name alpine1 --network test1 alpine:3.12.3
Hope that this might help someone :)
I'm using docker-compose.yml version 2. One of my containers doesn't see another one and I'm trying to debug this.
Previously, docker-compose relied on links mechanism for containers to interact with each other. It was implemented via dynamic modification of /etc/hosts file.
Starting from docker-compose version 2, docker-compose relies upon Docker DNS mechanism. Now /etc/hosts is kept intact and containers query their internal Docker DNS to find each other.
I wonder, how do I query Docker DNS from within a container for debugging purposes? I want to make sure that it properly resolves the hostname of other containers in its network and that they are known by their aliases.
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/
Docker allows servers from multiple containers to connect to each other via links and service discovery. However, from what I can see this service discovery is host-local. I would like to implement a service that uses other services hosted on a different machine.
There have been several approaches to solving this problem in Docker, such as CoreOS's jumpers, host-local services that essentially proxy to the other machine, and a whole bunch of github projects for managing Docker deployments that appear to have attempted to support this use-case.
Given the pace of development it is hard to follow what current best practices are. Therefore my question is essentially:
What (if any) is the current predominant method for linking across hosts in Docker, and
Are there any plans for supporting this functionality directly in the Docker system?
Update
Docker has recently announced a new tool called Swarm for Docker orchestration.
Swarm allows you do "join" multiple docker daemons: You first create a swarm, start a swarm manager on one machine, and have docker daemons "join" the swarm manager using the swarm's identifier. The docker client connects to the swarm manager as if it were a regular docker server.
When a container started with Swarm, it is automatically assigned to a free node that meets any constraints that have been defined. The following example is taken from the blog post:
$ docker run -d -P -e constraint:storage=ssd mysql
One of the supported constraints is "node" that allows you pin a container to a specific hostname. The swarm also resolves links across nodes.
In my testing I got the impression that Swarm doesn't yet work with volumes at a fixed location very well (or at least the process of linking them is not very intuitive), so this is something to keep in mind.
Swarm is now in beta phase.
Until recently, the Ambassador Pattern was the only Docker-native approach to remote-host service discovery. This pattern can still be used and doesn't require any magic beyond plain Docker in that the pattern consists of one or more additional containers that act as proxies.
Additionally, there are several third-party extensions to make Docker cluster-capable. Third-party solutions include:
Connecting the Docker network bridges on two hosts, lightweight and various solutions exist, but generally with some caveats
DNS-based discovery e.g. with skydock and SkyDNS
Docker management tools such as Shipyard, and Docker orchestration tools. See this question for an extensive list: How to scale Docker containers in production
UPDATE 3
Libswarm has been renamed as swarm and is now a separate application.
Here is the github page demo to use as a starting point:
# create a cluster
$ swarm create
6856663cdefdec325839a4b7e1de38e8
# on each of your nodes, start the swarm agent
# <node_ip> doesn't have to be public (eg. 192.168.0.X),
# as long as the other nodes can reach it, it is fine.
$ swarm join --token=6856663cdefdec325839a4b7e1de38e8 --addr=<node_ip:2375>
# start the manager on any machine or your laptop
$ swarm manage --token=6856663cdefdec325839a4b7e1de38e8 --addr=<swarm_ip:swarm_port>
# use the regular docker cli
$ docker -H <swarm_ip:swarm_port> info
$ docker -H <swarm_ip:swarm_port> run ...
$ docker -H <swarm_ip:swarm_port> ps
$ docker -H <swarm_ip:swarm_port> logs ...
...
# list nodes in your cluster
$ swarm list --token=6856663cdefdec325839a4b7e1de38e8
http://<node_ip:2375>
UPDATE 2
The official approach is now to use libswarm see a demo here
UPDATE
There is a nice gist for openvswitch hosts communication in docker using the same approach.
To allow service discovery there is an interesting approach based on DNS called skydock.
There is also a screencast.
This is also a nice article using the same pieces of the puzzle but adding also vlans on top:
http://fbevmware.blogspot.it/2013/12/coupling-docker-and-open-vswitch.html
The patching has nothing to do with the robustness of the solution. Docker is actually only a sort of DSL upon Linux Containers and both solutions in these articles simply bypass some Docker automatic settings and fall back directly to Linux Containers.
So you can use the solutions safely and wait to be able to do it in a simpler way once Docker will implement it.
Weave is a new Docker virtual network technology that acts as a virtual ethernet switch over TCP/UDP - all you need is a Docker container running Weave on your host.
What's interesting here is
Instead of links, use static IPs/hostnames in your virtual network
Hosts don't need full connectivity, a mesh is formed based on what peers are available, and packets will be routed multi-hop to where they need to go
This leads to interesting scenarios like
Create a virtual network across the WAN, none of the Docker containers will know or care what actual network they sit in
Move your containers to different physical docker hosts, Weave will detect the peer accordingly
For example, there's an example guide on how to create a multi-node Cassandra cluster across your laptop and a few cloud (EC2) hosts with two commands per host. I launched a CoreOS cluster with AWS CloudFormation, installed weave on each in /home/core, plus my laptop vagrant docker VM, and got a cluster up in under an hour. My laptop is firewalled but Weave seemed to be okay with that, it just connects out to its EC2 peers.
Update
Docker 1.12 contains the so called swarm mode and also adds a service abstraction. They probably aren't mature enough for every use case, but I suggest you to keep them under observation. The swarm mode at least helps in a multi-host setup, which doesn't necessarily make linking easier. The Docker-internal DNS server (since 1.11) should help you to access container names, if they are well-known - meaning that the generated names in a Swarm context won't be so easy to address.
With the Docker 1.9 release you'll get built in multi host networking. They also provide an example script to easily provision a working cluster.
You'll need a K/V store (e.g. Consul) which allows to share state across the different Docker engines on every host. Every Docker engine need to be configured with that K/V store and you can then use Swarm to connect your hosts.
Then you create a new overlay network like this:
$ docker network create --driver overlay my-network
Containers can now be run with the network name as run parameter:
$ docker run -itd --net=my-network busybox
They can also be connected to a network when already running:
$ docker network connect my-network my-container
More details are available in the documentation.
The following article describes nicely how to connect docker containers on multiple hosts: http://goldmann.pl/blog/2014/01/21/connecting-docker-containers-on-multiple-hosts/
It is possible to bridge several Docker subnets together using Open vSwitch or Tinc. I have prepared Gists to show how to do it:
Open vSwitch: https://gist.github.com/noteed/8656989
Tinc: https://gist.github.com/noteed/11031504
The advantage I see using this solution instead of the --link option and the ambassador pattern is that I find it more transparent: there is no need to have additional containers and more importantly, no need to expose ports on the host. Actually I think of the --link option to be a temporary hack before Docker get a nicer story about multi-host (or multi-daemon) setups.
Note: I know there is another answer pointing to my first Gist but I don't have enough karma to edit or comment on that answer.
As mentioned above, Weave is definitely a viable solution to link Docker containers across the hosts. Based on my own experience with it, it is fairly straightfoward to set it up. It is now also has DNS service which you can address container's by its DNS names.
On the other hand, there is CoreOS's Flannel and Juniper's Opencontrail for wiring the containers across the hosts.
Seems like docker swarm 1.14 allows you to:
assing hostname to container, using --hostname tag, but i haven't been able to make it work, containers are not able to ping each other by assigned hostnames.
assigning services to machine using --constraint 'node.hostname == <host>'