I have a silly question regarding docker swarm.
I am thinking I can start a web application image in two containers, either in same server or two vm servers, then I start a load balance container, pointing to two web app containers through IP and port.
In this case, why do I need docker swarm for clustering management? What benefits can docker swarm bring?
I have read from docker documentation, they only introduce what is swarm and how to use swarm. But I can not find out answer for why I have to use swarm.
Thanks
What is swarming managing? turns a pool of Docker hosts into a single, virtual Docker host.
Can swarm auto-start the container if the container died? Yes it can, so can the Docker daemon on each host.
Can swarm auto-create more nodes if the resource is not enough? No it cannot. It does not aims on providing this service. Nevertheless you can program a node that start and run containers when needed.
Which mean, if traffic grows fast, do we still manually create more node and deploy more containers? Yes, unfortunately.
update
If needed, here is an answer that details how to deploy a Swarm cluster.
Related
I've managed to run Docker Swam mode with multiple hosts with Docker Toolbox, but I am unable to create a swarm with Docker Desktop since it apparently only offers single node swarm.
Is there any way to get this working with Docker Desktop or is it not supported?
No. But yes. But actually no. But technically yes.
No. Docker Desktop does not support this. It manages a single docker node in a vm and has no capability to manage multiple dockers.
But yes. docker:dind is an image you can easily use to deploy multiple docker nodes as containers, and then swarm init / swarm join to create a swarm cluster hosted on docker. You can even swarm join the docker-desktop node to be the swarm manager which means you can communicate with your local docker desktop node to control the swarm.
But actually, no.
Unless your use case is a very limited hello-world on swarm tutorial, there is no support for exposing ports from the dind-swarm to the host. Even if the host docker acts as the manager, overlay networking that is required for ingress will require communications over :2377, :4789/udp, and :7946, and as the host is not part of its own overlay networks, this will never work.
So, communicating with tasks running on the swarm is basically impossible.
But technically yes. play-with-docker apparently runs docker swarms using dind. They do some heavy lifting to expose a restricted set of ports via l7 loadbalancers. Pretty cool. but not at all easy to do at home. If you have a spare Dell PowerEdge or equivalent blade server with 120+ cores just laying around, and want to expose it as a docker swarm rather than split it into VMS... perhaps this is a viable approach.
I need to setup a cluster of nodes using Docker Swarm. When I say a node, it should have a db, few apps/services and they need to commuicate with each other. I can create a single instance of this using Docker Compose.
But, I need multiple instances of this setup. So, would Docker Swarm help?
When I say a node, it should have a db, few apps/services and they need to commuicate with each other
Docker Swarm is a tool for managing cluster of nodes, when node is a machine (VM/physical) with docker installed. it's not clear what you expect "node" to be, but with swarm you can run any number of containers which will be deployed across the different machines in the cluster.
But, I need multiple instances of this setup. So, would docker swarm help?
You can define anything on the cluster, but basically swarm is meant to enable communication between the nodes. if you want all your services (which you call "node") to be on the same machine anyway, so swarm will not give you any benefits. just copy-paste the docker compose file between all your nodes. But this isn't something common/recommended in general so maybe if you'll explain better your needs, it would be easier to help you.
I am new to cluster container management, and this question is the basis for all the freshers over here.
I read some documentation, but still, my understanding is not too clear, so any leads.. helping to understand?
Somewhere it is mentioned, Minikube is used to run Kubernetes locally. So if we want to maintain cluster management in my four-node Raspberry Pi, then Minikube is not the option?
Does Minikube support only a one-node system?
Docker Compose is set of instructions and a YAML file to configure and start multiple Docker containers. Can we use this to start containers of the different hosts? Then for simple orchestration where I need to call container of the second host, I don't need any cluster management, right?
What is the link between Docker Swarm and Kubernetes? Both are independent cluster management. Is it efficient to use Kubernetes on Raspberry Pi? Any issue, because I was told that Kubernetes in single node takes the complete memory and CPU usage? Is it true?
Is there other cluster management for Raspberry Pi?
I think this 4-5 set will help me better.
Presuming that your goal here is to run a set of containers over a number of different Raspberry Pi based nodes:
Minikube isn't really appropriate. This starts a single virtual machine on a Windows, MacOS or Linux and installs a Kubernetes cluster into it. It's generally used by developers to quickly start-up a cluster on their laptops or desktops for development and testing purposes.
Docker Compose is a system for managing sets of related containers. So for example if you had a web server and database that you wanted to manage together you could put them in a single Docker Compose file.
Docker Swarm is a system for managing sets of containers across multiple hosts. It's essentially an alternative to Kubernetes. It has fewer features than Kubernetes, but it is much simpler to set up.
If you want a really simple multi-node Container cluster, I'd say that Docker swarm is a reasonable choice. If you explicitly want to experiment with Kubernetes, I'd say that kubeadm is a good option here. Kubernetes in general has higher resource requirements than Docker Swarm, so it could be somewhat less suited to it, although I know people have successfully run Kubernetes clusters on Raspberry Pis.
Docker Compose
A utility to to start multiple docker containers on a single host using a single docker-compose up. This makes it easier to start multiple containers at once, rather than having do mutliple docker run commands.
Docker swarm
A native container orchestrator for Docker. Docker swarm allows you to create a cluster of docker containers running on multiple machines. It provides features such as replication, scaling, self-healing i.e. starting a new container when one dies ...
Kubernetes
Also a container orchestrator. Kubernetes and Docker swarm can be considered as alternatives to one another. They both try to handle managing containers starting in a cluster
Minikube
Creating a real kubernetes cluster requires having multiple machines either on premise or on a cloud platform. This is not always convenient if someone is just new to Kubernetes and trying to learn by playing around with Kubernetes. To solve that minikube allows you to start a very basic Kubernetes cluster that consists of a single VM on you machine, which you can use to play around with Kubernetes.
Minikube is not for a production or multi-node cluster. There are many tools that can be used to create a multi-node Kubernetes cluster such as kubeadm
Containers are the future of application deployment. Containers are smallest unit of deployment in docker. There are three components in docker as docker engine to run a single container, docker-compose to run a multi-container application on a single host and docker-swarm to run multi-container application across hosts which also an orchestration tool.
In kubernetes, the smallest unit of deployment is Pod(which is composed of multiple container). Minikube is a single node cluster where you can install it locally and try, test and feel the kubernetes features locally. But, you can't scale this to more than a single machine. Kubernetes is an orchestration tool like Docker Swarm but more prominent than Docker Swarm with respect to features, scaling, resiliency, and security.
You can do the analysis and think about which tool will be fit for your requirements. Each one having their own pros or cons like docker swarm is good and easy to manage small clusters whereas kubernetes is much better for larger once. There is another orchestration tool Mesos which is also popular and used in largest size clusters.
Check this out, Choose your own Adventure but, it's just a general analogy and only to understand because all the three technologies are evolving rapidly.
I get the impression you're mostly looking for confirmation and am happy to help with that if I can.
Yes, minikube is local-only
Yes, minikube is intended to be single-node
Docker-compose isn't really an orchestration system like swarm and Kubernetes are. It helps with running related containers on a single host, but it is not used for multi-host.
Kubernetes and Docker Swarm are both container orchestration systems. These systems are good at managing scaling up, but they have an overhead associated with them so they're better suited to multi-node.
I don't know the range of orchestration options for Raspberry Pi, but there are Kubernetes examples out there such as Build Your Own Cloud with Kubernetes and Some Raspberry Pi.
For Pi, you can use Docker Swarm Mode on one or more Pi's. You can even run ARM emulation for testing on Docker for Windows/Mac before trying to get it all working directly on a Pi. Same goes for Kubernetes, as it's built-in to Docker for Windows/Mac now (no minikube needed).
Alex Ellis has a good blog on Pi and Docker and this post may help too.
I've been playing around with orchestrating Docker containers on a subnet of Raspberry Pis (3Bs).
I found Docker-swarm easiest to set up and work with, and adequate for my purposes. Guide: https://docs.docker.com/engine/swarm/swarm-tutorial/
For Kubernetes there are two main options; k3s and microk8s. Some guides:
k3s
https://bryanbende.com/development/2021/05/07/k3s-raspberry-pi-initial-setup
microk8s
https://ubuntu.com/tutorials/how-to-kubernetes-cluster-on-raspberry-pi#1-overview
i'm learning about docker swarm, and got confused about the swarm discovery option, i see that lots of tutorials on internet use this option to create containers with docker-machine, but when i enter the documentation on docker swarm doc it says:
You are viewing docs for legacy standalone Swarm. These topics describe standalone Docker Swarm. In Docker 1.12 and higher, Swarm mode is integrated with Docker Engine. Most users should use integrated Swarm mode.
So, what are the use cases for the discovery options? All the tutorials use the docker-machine to create a swarm, i always need it or can just install the docker on machines in my cluster, join them in swarm and use normal?
I saw some names like Docker Swarm and Docker Swarm Mode, are there any difference or just different ways to call the same feature?
Q. Docker Swarm discovery is still relevant?
A: No, if you use docker Swarm Mode and an overlay network (see below)
Q. Are there any difference between Docker Swarm and Docker Swarm Mode?
A: Yes, TL;DR Docker Swarm is deprecated and should not be used anymore, Docker Swarm Mode (we should just say Swarm Mode) is the recommended way of clustering containers and have reliability, load-balancing, scaling, and rolling service upgrades.
Docker Swarm (official doc) :
is the old fashioned way (<1.12) of clustering containers
uses a dedicated container for building a Docker Swarm cluster
needs a discovery service like Consul to reference containers in cluster
Swarm Mode (official doc):
is the new and recommended way (>=1.12) of clustering containers on host nodes (called managers / workers)
is built-in in Docker engine, you don't need an additional container
has a built-in discovery service if you use an overlay network (DNS resolution is done within this network), you don't need an additional container
You can have a look to this SO thread on same topic.
Q. Do i always need docker-machine to create a swarm?
A: No, docker-machine is a helper to create virtual hosts in the cloud like amazon ec2, azure, digitalocean, google, openstack..., or your own network with virtual box.
To create a Swarm Mode, you need :
a multiple hosts cluster with docker engine installed on each host (called node) (that is what docker-machine facilitates)
run docker swarm init to switch to Swarm Mode on your first manager node
run docker swarm join on worker nodes to add them in the cluster
There are some subtle adjustments to Swarm mode to increase high availability (recommended number of managers in the swarm, node placement in multiple availability zones in the cloud)
Hope this helps!
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.