I worked with https://labs.play-with-docker.com.
I created a new service in one of the managers (not the leader):
docker service create --name example nginx
When I ran:
docker container ls
It didn't show me the containers:
But when I ran the same command on the manager leader node, it did:
Any explanation why is that ?
You have created a service that is replicated only once (one container), if you want a global service (a container in each VM) you have to add --mode global flag to you docker service create command, by the way you take a look at --replicas flag too : https://docs.docker.com/engine/swarm/services/
Related
I have a docker swarm node running a set of docker services connected by a overlay network. When needed I dynamically add another docker node via terraform . It'll be a separate ec2 instance setup and connected as a worker node to the existing swarm network.
I'll run a container from my manager and the running container needs to talk to the existing services in manager node. For eg: Connecting to postgres service and running few queries.
docker -H <node ip> run --network <overlay network where services are running> <some image> <command>
The script running in the container fails with "Name or service not known" error. I tried to manually ping by bashing into the container and ping succeeds after some 4 or 5 seconds. I tried this hundreds of times and I always get the same issue. Also, it doesn't matter when the node is joined to the swarm. Every time I run the above command, I face the same issue.
Also, I don't have control over what script is run in the container so I cannot add retries.
One more thing. Sometimes, some services can be reached immediately. For eg., Postgres will fail. But another service exposing rest end points can be reached. But it's not always the case.
I was able to reproduce this issue with a bunch of test services:
Steps to reproduce the issue:
Create a docker swarm and add another machine as a worker node to
docker swarm
Create a overlay network in node 1 docker network create -d overlay --attachable platform
Create services in node 1 for i in {1..25} do docker service create --network platform -p :80 --name "service-${i}"
dockerbogo/docker-nginx-hello-world done
Create a task from node 1 to be run in node 2 docker -H 10.128.0.3:2376 run --rm --network platform centos ping service-1
Docker daemon logs: https://pastebin.com/65Lihp8v
Any help?
I have docker on my host machine with a container running. I was wondering if it's possible, and what the best approach would be, to "trigger" a container creation from the running container.
Let's say my machine is host and I have a container called app (with id 123456789) running on host.
root#host $ docker contain ls
123456789 app_mage .... app
I would like to create a container on host from within app
root#123456789 $ docker run --name app2 ...
root#host docker container ls
123456789 app_mage .... app
12345678A app_mage .... app2
What I need is for my app to be running on docker and to run arbitrary applications in an isolated environment (but I'd rather avoid docker-in-docker)
A majority of the Docker community will veer away from these types of designs, however it is very doable.
Similar to Starting and stopping docker container from other container you can simply mount the docker.sock file from the host machine into the container, giving it privilege to access the docker daemon.
To make things more automated, you could use the docker-py sdk to start containers from inside a container, which would in turn access the Docker deamon on the host machine hosting the container that you are spawning more containers from.
For example:
docker run -v /var/run/docker.sock:/var/run/docker.sock image1 --name test1
----
import docker
def create_container():
docker.from_env().containers.run("image2", name="test2")
This example starts container test1, and runs that method inside the newly created container, which in turn creates a new container test2 running on the same host as test1.
I'm trying to setup some very simple networking between a pair of Docker containers and so far all the documentation I've seen is far more complex than for what I am trying to do.
My use case is simple:
Container 1 is already running and is listening on port 28016
Container 2 will start after container 1 and needs to connect to container 1 on port 28016.
I am aware I can set this up via Docker-Compose with ease, however Container 1 is long-lived and for this use case, I do not want to shut it down. Container 2 needs to start and automatically connect to container 1 via port 28016. Also, both containers are running on the same machine. I cannot figure out how to do this.
I've exposed 28016 in Container 1's dockerfile, and I'm running it with -p 28016:28016. What do I need to do for Container 2 to connect to Container 1?
There are a few ways of solving this. Most don't require you to publish the ports.
Using a user defined network
If you start your long-running container in a user-defined network, because then docker will handle
docker network create service-network
docker run --net=service-network --name Container1 service-image
If you then start your ephemeral container in the same network, it will be able to refer to the long-running container by name. E.g:
docker run --name Container2 --net=service-network ephemeral-image
Using the existing container network namespace
You can just run the ephemeral container inside the network namespace of the long running container:
docker run --name Container2 --net=container:Container1 ephemeral-image
In this case, the service would be available via localhost:28016.
Accessing the service on the host
Since you've published the service on the host with -p 28016:28016, you can refer to that access using the address of the host, which from inside the container is going to be the default gateway. You can get that with something like:
address=$(ip route | awk '$1 == "default" {print $3}')
And your service would be available on ${address}:28016.
Here are the steps to perform:
Create a network: docker network create my-net
Attach the network to the already running container: docker container attach <container-name> my-net
Start the new container with the --network my-net or with docker-compose add a network property:
...
networks:
- my-net
networks:
my-net:
external: true
The container should now be able to communicate using the container-name as a DNS host name
I am very new to docker , just started venturing into this. I read online about this. I came to know of the following commands of docker which is: docker run and docker service. As I understood , with docker run we are spinning a new container. However I am not clear what docker service do? Does it spin container in a Swarm?
Can anyone help understand in simple to understand?
The docker run command creates and starts a container on the local docker host.
A docker "service" is one or more containers with the same configuration running under docker's swarm mode. It's similar to docker run in that you spin up a container. The difference is that you now have orchestration. That orchestration restarts your container if it stops, finds the appropriate node to run the container on based on your constraints, scale your service up or down, allows you to use the mesh networking and a VIP to discover your service, and perform rolling updates to minimize the risk of an outage during a change to your running application.
Docker Run vs Docker service
docker run:
we can create number of containers with different images.
docker service:
we can create number of containers with same image in a single command line.
SYNTAX:
docker service create --name service-name --network network-name --replicas number-of-containers image-name
EXAMPLE:
docker service create --name service1 --network swarm-net --replicas 5 redis
I run a docker swarm with docker swarm mode. Let's say I have 4 nodes, 1 manager, 3 worker. The hostnames are:
manager0
worker0
worker1
worker2
I start the service in global mode, so every node runs the service once.
Let's say the command looks like this:
docker service create --name myservice --mode global --network mynetwork ubuntu wait 3600
mynetwork is an overlay network.
Now I am trying to access the hostname of the docker host in the containers, so I can pass the hostname to an application in the container.
I tried to pass the hostname with the environment variables (--env hostname=$(hostname)), but actually ${hostname} is only executed on the manager and the hostname is set to manager0 for all nodes.
Is there a way to access the hostname or pass the hostname to the containers?
You can use latest naming templates to create service with hostname.
Here is the feature request, that has been implemented in docker version 17.10
https://github.com/moby/moby/issues/30966