With the release of docker 1.9 came container networks. I understand how to use them but i'm not sure why I should use them. what are the benefits of using container networks?
The main reason I uses container networks is so that I can give the containers the same IP's as real virtual machines. I use docker a lot to test salt-stack states. I put all the machines I want into a docker-compose file and use docker images with salt-master / salt-minion installed. I apply my states and I have a working copy of the target environment.
There are two main benefits: containers isolation and communication in a clustered environment.
"Container networks" are virtual networks; they work on top of existing physical networks but allow you to create private networks that are only visible to the containers who are on that network. This isolation is an important security feature. You typically place all of your backend container services like database, indexing, app server in their own private network and only expose one container (nginx, apache, haproxy,...) to the outside world (public network).
Virtual networks also allow the creation of overlay networks, which permits containers in different hosts to communicate as if they we were on the same host. This is the basis for clustered solution like Docker Swarm.
Related
I have two instances of keycloak running on container each on is running on a single node.
The nodes are bare-metal nodes inside my company network.
keycloak uses TCPPING as discovery protocol.
Since the two containers are running on different nodes, and each instance is pining inside docker default network they are not able to find each other.
I said docker default network because I didn’t specify special network for the two containers.
Any idea how can I make the two instances in this architectural design discover each others!
and I was thinking about docker swarm as a solution.
Assuming the two nodes are on the same network and are able to connect to each other, you can get the two container to discover each other using docker host networking
It would be as easy as docker run --net=host
Docker host networking makes the container to use the networking of the host node and thus will be allocated an IP address by the DHCP server used by the host node and for all practical purposes , would look like another host in that network.
This allows the two containers to discover each other using TCPPING
Docker swarm would also enable this .Docker swarm basically abstracts multiple host nodes such that you can containers on them as if you are running docker on single host. But that will require docker-machine and whole new setup.
I am working on a research project where I have to create an architecture of a number of worker nodes and a master node.
I want to write load balancing algorithm and test on these nodes(they have applications running on them). I have started studying Docker and I want to use it to create the architecture.
I am unable to decide which network type to use, as docker networking structure is quiet vast. They have created lot of abstractions over the Linux network drivers.
Should I use a bridge or an overlay network?
I want all worker node to send their CPU and memory usage to the master node. Basically worker can talk to the master. Then I will write load balancing algorithms over the master container node.
Need guidance from a networking expert in Docker. Thanks in advance.
If you have a single-host setup then you generally should use "bridge". (You should declare some network in this case to take advantage of the inter-container DNS.)
If you have a multi-host setup then there are many setups you can use; valid options include Docker Swarm, Hashicorp's Nomad, Kubernetes, a hand-built setup around a service-discovery intermediary like Consul, or a hand-built setup where each directly service knows about the other nodes' host names and ignores the Docker layer.
If you are using Docker Swarm then you need to use "overlay". But each of the options I described above uses a different networking setup (Kubernetes uses a piece called CNI, and there are a dozen different implementation choices within this, for instance) and this question isn't directly meaningful for many of them.
As you're describing the project it sounds like you want to explicitly place applications on specific nodes, and manage the routing between them manually. For this I'd probably use "bridge" networking only: launch Docker containers using -p (or Docker Compose ports:) options to publish ports on the host IP addresses, and communicate between containers using only those host IP addresses. That will give you a useful level of manual control for a research project.
I have a couple of Docker swarm questions (Sorry for not splitting them up but they are all closely related):
Do all instances in a swarm have to run on different machines or can they all run on the same? (if having limited amount of hardware and just wanting to try swarm mode)
Do I have to run swarm mode to be able to communicate between instances?
What is the key difference between swarm mode and just running a number of containers as regular?
What are the options of communication between instances of containers? (in swarm and in regular mode) http? named pipes? other?
If using http communication between containers on same machine, will it be roughly similarly as fast as named pipes?
Is there any built in support for a message bus or similar in Docker?
Is there support for any consensus protocol in Docker?
Are there any GUI's for designing, managing, testing and/or debugging Docker swarms?
Can a container list other containers, stop/restart some and start new ones? (to be able to function as a manager for other containers)
Can a container be given access to OS-features (Linux in my case) to configure for instance a reverse proxy or port forwarding on the WAN?
Background: What I'm trying to figure out is how I should go about and build a micro service mesh using Docker. The containers will be running .NET Core. I'm not too keen on relying too much on specifically Docker since it may not be the preferred tech in a couple of years. What can/should I do with Docker and what can/should I do inside the containers. That's what I'm trying to figure out.
I've copied your questions and tried to answer them.
Do all instances in a swarm have to run on different machines or can they all run on the same? (if having limited amount of hardware and just wanting to try swarm mode)
You can have only one machine in a swarm and run multiple tasks of the same service or in other words your scale of a service can be more than the number of actual machines. I have a testing swarm with a single machine and one with three and it works the same way.
Do I have to run swarm mode to be able to communicate between instances?
You have to run your docker in swarm mode in order to create a service, please see this link
What is the key difference between swarm mode and just running a number of containers as regular?
The key difference afaik is, that when a task goes down, docker puts another task up automatically. And you can easily scale your services, which means you can easily have multiple tasks just by scaling your service (up or down). As of running a container - when it goes down you have to manually start another.
What are the options of communication between instances of containers? (in swarm and in regular mode) http? named pipes? other?
I've currently only tested with a couple of wildfly servers in a swarm, which are on the same network. I'm not sure about others, but would love to find out. I've only read about RabbitMQ, but can't seem to find the link atm.
If using http communication between containers on same machine, will it be roughly similarly as fast as named pipes?
I can't say.
Is there any built in support for a message bus or similar in Docker?
I can't say.
Are there any GUI's for designing, managing, testing and/or debugging Docker swarms?
I've tested rancher and portainer.io, for a list of them I found this link
Can a container list other containers, stop/restart some and start new ones?
I'm not sure why would you want to do that? And I guess it's possible, see this link
Can a container be given access to OS-features (Linux in my case) to configure for instance a reverse proxy or port forwarding on the WAN?
I can't say.
#namokarm did a great job, and I'm filling in the gaps:
Benefits of Swarm over docker run or docker-compose.
All communications between containers has to be TCP/UDP etc. You could force two containers to only run on a single machine, then bind-mount their socket so they skip the network, but that would be a bit of an anti-pattern. Swarm is designed for everything to be distributed and TCP/UDP.
In a few cases, such as PHP-FPM + Nginx, I recommend bundling both in the same container (against docker best practices, but trust me it's easier than separate containers). This will ensure they scale together (1-to-1 relationship) and stay fast since they use local sockets to communicate). I only recommend this for a few setups like this, the other being ColdFusion + Nginx because they are two parts of the same tool that provide a HTTP response... I don't recommend bundling images together in nearly all other cases, but I'm open to ideas :).
Rancher is no longer supporting Swarm. Portainer and SwarmPit are GUI options.
Yes a container running something like Portainer/SwarmPit or controlling the Docker socket through a bind-mount or TCP can control the whole Swarm. This is how all docker management works :)
For reverse proxy, you would run a container-based proxy like Traefik or Docker Flow Proxy, which sets up HAProxy for Docker and Swarm.
Many of these topics are discussed in my DockerCon talks: https://www.bretfisher.com/dockercon18/
I'm wondering whether there are any differences between the following docker setups.
Administrating two separate docker engines via the remote api.
Administrating two docker swarm nodes via one single docker engine.
I'm wondering if you can administrate a swarm with the ability run a container on a specific node are there any use cases to have separate docker engines?
The difference between the two is swarm mode. When a docker engine is running services in swarm mode you get:
Orchestration from the manager to continuously try to correct any differences between the current state and the target state. This can also include HA using the quorum model (as long as a majority of the managers are reachable to make decisions).
Overlay networking which allows containers on different hosts to talk to each other on their own container network. That can also involve IPSEC for security.
Mesh networking for published ports and a VIP for the service that doesn't change like container IP's do. The latter prevents problems from DNS caching. And the former has all nodes in the swarm publish the port and routes traffic to a container providing this service.
Rolling upgrades to avoid any downtime with replicated services.
Load balancing across multiple nodes when scaling up a service.
More details on swarm mode are available from docker's documentation.
The downside of swarm mode is that you are one layer removed from the containers when they run on a remote node. You can't run an exec command on a task to investigate a container, you need to do that on a container and be on the node it's currently using. Docker also removed some options from services like --volumes-from which don't apply when containers may be running on different machines.
If you think you may grow beyond running containers on a single node, need to communicate between the containers on different nodes, or simply want the orchestration features like rolling upgrades, then I would recommend swarm mode. I'd only manage containers directly on the hosts if you have a specific requirement that prevents swarm mode from being an option. And you can always do both, manage some containers directly and others as a service or stack inside of swarm, on the same nodes.
I'm trying to understand the differences or similarities between Docker-Compose and Docker-Swarm.
By reading the documentation I have understood that docker-compose provides a mechanism to bind different containers together and work in collaboration, as a single service (I'm guessing it's using the same functionality as --link command used to link two containers)
Also, my understanding of docker-swarm is that it allows you to manage a cluster of different docker-hosts, each of which is running several container instances of some docker-images. We could define connections as overlay-networks between different containers in the swarm (even if they across two docker-hosts in the swarm) to connect them as a unit.
What I'm trying to understand is has docker-swarm succeeded docker-compose and overlay networks is the new (recommended) way to connect containers?
Or is it that docker-compose is still an integral part of the entire docker family and it is expected and advisable to use it to connect containers to work in collaboration. If so does docker-compose work with containers across different nodes in the swarm??
Or is it that overlay networks is for connecting containers across different hosts in the swarm and docker-compose is for creating internal links??
Besides I also see that it is mentioned in the docker documentation that --links not recommended anymore and will be obsolete soon.
I'm a bit confused???
Thanks Alot!
It will probably help to start with a few definitions:
docker-compose: Command used to configure and manage a group of related containers. It is a frontend to the same api's used by the docker cli, so you can reproduce it's behavior with commands like docker run.
docker-compose.yml: Definition file for a group of containers, used by docker-compose and now also by swarm mode.
swarm mode: Used to manage a group of docker engines as a single entity and provide orchestration (constantly trying to correct any differences between the current state and the target state).
service: One or more containers for the same image and configuration within swarm, multiple containers provide scalability.
stack: One or more services within a swarm, these may be defined using a DAB or a docker-compose.yml file.
bridge network: Network managed by a single docker engine where multiple containers may communicate with each other. You may have multiple networks managed by an engine, and containers can be attached to zero or more networks.
overlay network: Similar to a bridge network but spanning multiple docker engines. These require a key/value store to maintain their state. Swarm mode provides this, but if swarm mode is disabled, you may also use etcd, consul, or zookeeper.
links: a method to connect containers together that predates the bridged network. Its usage is no longer recommended.
classic swarm: A predecessor to the integrated swarm mode that runs as a container, allows multiple engines to appear as one, but does not provide orchestration or include its own k/v store.
To answer the questions:
has docker-swarm succeeded docker-compose and overlay networks is the new (recommended) way to connect containers?
Or is it that docker-compose is still an integral part of the entire docker family and it is expected and advisable to use it to connect containers to work in collaboration. If so does docker-compose work with containers across different nodes in the swarm??
They provide different functionality and will continue to both serve a purpose. docker-compose cannot start containers inside swarm mode, but a newer version of the docker-compose.yml file (version 3) can be used to define a stack directly in swarm mode without using docker-compose itself. docker-compose is needed to manage containers outside of swarm mode, on a single docker engine or with classic swarm.
Or is it that overlay networks is for connecting containers across different hosts in the swarm and docker-compose is for creating internal links??
Besides I also see that it is mentioned in the docker documentation that --links not recommended anymore and will be obsolete soon.
docker-compose starting with version 2 of the yml file connects multiple containers together by default with a new bridged network per project (the project defaults to the directory name). With classic swarm, that would default to an overlay network using an external k/v store. And with a swarm mode stack, this would be an overlay network.
Using docker networks is the preferred way to have containers communicate with each other. You want a network per group of containers you wish to isolate from the rest of your docker environment. docker-compose automates this network creation, but you can also do it from the command line with docker networks create.
Linking have been largely replaced by docker networks with built-in DNS discovery. When you remove links from your docker-compose.yml, you may need to replace them with a depends_on section to enforce container startup order. Otherwise, there are very few scenarios where linking makes sense and all the usage I've seen is from someone following outdated documentation.
compose or swarm or swarm overlay networks
You would find that you need to use all of the above if you're doing anything other than a demo on your laptop etc.
I deliberately separated out swarm & swarm overlay networks, because you need not use both, but you cannot get an overlay network without having a swarm underneath it.
Compose is for bringing up multiple containers together. Now it makes sense that they are related to each other, although they may not be. But let's suppose a typical case when the containers are for services that are related to each other, then you would want them to talk to each other in some way, but yet control how they talk to each other using networks. For example, take a 3 tier app that has a webserver, appserver and db. Let's say all three components are dockerized and you are using compose to bring them up togetherm instead of running docker run.. three times with different parameters etc. All three would come up, but you would want to control how they connect to each other. You want the webserver to be able to talk to the appserver, but not to the db directly. And you would want the appserver to talk (ping) the db server container and also ping the web server. All connections are two way, but restricted to only those services that you want to be able to communicate with each other. For such an arrangement, you would typically setup 2 networks - say frontend and backend. The web and app containers are connected to the frontend network. The app and db containers are connected to the backend network. Because there is no common network between the db and web containers they cannot touch (ping) each other, which is your intent.
Now, if you want these 3 services to be able to run on your cluster of 100's of machines, and you also want to scale across them, you would need a network that spans multiple hosts. That is where overlay networking (in swarm) comes into picture. Overlay networking is nothing but multi-host networking build over VxLAN technology. You do not have to know about VxLAN, except that it is a standard network topology that is supported in almost all modern networking infrastructure.
I hope that clarifies.
Edit: I did not see that you got an answer already!
I think you have most of the understanding correct as to what each is, but some tweaking is required.
You're correct docker-compose is to bring up multi-container applications. Earlier you used to do docker run .. to start every container. Usually modern applications embracing the micro-services paradigm can be made up of dozens of services and using docker run .. will get very tiresome very soon. Hence docker-compose allows you to express all the containers and their properties and how they connect to each other as a yaml or json file so you can manage it in an easier fashion.
So, docker-compose is the container orchestration part in the docker ecosystem.
Links are different, they are just a part of docker-compose or docker run commands and are deprecated in favor of software defined networks of which overlay networks are just one of them.
Swarm is the scheduling component in docker. What is scheduling - it is nothing but figuring out where to "place" your containers in your cluster of docker hosts. You can have a cluster of hundreds of servers, and you may have hundreds of containers, each encapsulating a service for a dozen different applications. Now how should these containers be distributed across your cluster of hundreds of servers, should some containers be placed only on certain hosts because they satisfy a particular criteria or maybe they should be closer to (or not) other containers which are somehow related... all these are part of the scheduling component which is performed by docker Swarm.
I suggest you go through the getting started documentation on docker.com here: https://docs.docker.com/engine/getstarted-voting-app/