{"componentChunkName":"component---src-templates-blog-post-js","path":"/docker-training/","result":{"data":{"site":{"siteMetadata":{"title":"Nans' blogs"}},"markdownRemark":{"id":"8657fc98-1466-5474-bf13-e588e4bf0fd1","excerpt":"Docker Essentials: A developer introduction Lab 1 : Running a container  What are Containers ? A group of precesses, run in isolation. They run on a shared…","html":"

Docker Essentials: A developer introduction

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Lab 1 : Running a container

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 What are Containers ?

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A group of precesses, run in isolation. They run on a shared kernel.\nThe isolation is provided by Linux namespaces.

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VM vs Container\nVMs are heavy and slow to start because they have a full OS.\n\n \n \n \n \n \ncontainers can be directly run on top of virtual machines.

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What is Docker ?

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Docker is tooling to manage containers.\n“build once, run anywhere”

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Why containers are appealing

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Running a container

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docker container run -t ubuntu top
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The docker run command first starts a docker pull to download the Ubuntu image onto your host. After it is downloaded, it will start the container.

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Even though we are using the Ubuntu image, it is important to note that the container does not have its own kernel. It uses the kernel of the host and the Ubuntu image is used only to provide the file system and tools available on an Ubuntu system.

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docker container ls\nCONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES\n\n        ubuntu              \"top\"               58 seconds ago      Up 58 seconds                           wizardly_germain
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then

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$ docker container exec -it 7d1a9d47e601 bash\nroot@7d1a9d47e601:/#
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Using docker container exec with bash is a common way to inspect a Docker container.

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Namespaces are a feature of the Linux kernel. However, Docker allows you to run containers on Windows and Mac. The secret is that embedded in the Docker product is a Linux subsystem.

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2. Run multiple containers

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running an nginx server :

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docker container run --detach --publish 8080:80 --name nginx nginx
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--detach flag will run this container in the background.\nthe publish flag publishes port 80 in the container by using port 8080 on your host.

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So here, go to localhost:8080 :\n\n \n \n \n \n

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The name flag names the container.

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Then, we can run another container :

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docker container run --detach --publish 8081:27017 --name mongo mongo:3.4
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We can see the containers by running docker container ls.

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Removing containers

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  1. \n

    Stop the containers :

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    docker container stop <container-id>
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    2. \n
  2. \n

    Remove the stopped containers :

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    docker system prune
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    3. \n
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⚠️ Note :\nYou should avoid using unverified content from the Docker Store when developing your own images because these images might contain security vulnerabilities or possibly even malicious software.

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Lab 2 Add CI/CD value with Docker images

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Docker images

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Docker registry push and pull image from registry.\nDefault registry: Docker hub. Public and free for public images.

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You can also have a private registry, self-hosted, or cloud provider options.

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Creating a docker image - with Docker build

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Secret Sauce: Docker image layers

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Deploy a change

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Update app.py by changing “Hello World” with “Hello Beautiful World!“.

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Rebuild the image

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docker image build -t nansdibm/python-hello-world .
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Notice the “Using cache” for Steps 1 - 3. These layers of the Docker image have already been built, and the docker image build command will use these layers from the cache instead of rebuilding them.

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docker push nansdibm/python-hello-world
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The push refers to repository [docker.io/nansdibm/python-hello-world]\nbd3dadabc6d3: Pushed\n455874a92037: Layer already exists\n5f354b8b5dc0: Layer already exists\nf61107386c17: Layer already exists\ndb49993833a0: Layer already exists\n58c71ea40fb0: Layer already exists\n2b0fb280b60d: Layer already exists
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There is a caching mechanism in place for pushing layers too. Docker Hub already has all but one of the layers from an earlier push, so it only pushes the one layer that has changed.

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 Understanding image layers

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FROM python:3.6.1-alpine\nRUN pip install flask\nCMD ["python","app.py"]\nCOPY app.py /app.py
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Each of these lines is a layer. Each layer contains only the delta, or changes from the layers before it. To put these layers together into a single running container, Docker uses the union file system to overlay layers transparently into a single view.

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The “copy-on-write” function is very fast and in almost all cases, does not have a noticeable effect on performance. You can inspect which files have been pulled up to the container level with the docker diff command. For more information, see the command-line reference on the docker diff command.

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docker diff 0a8fa98d3b93
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Because image layers are read-only, they can be shared by images and by running containers.

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\n \n \n \n \n

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Because the containers use the same read-only layers, you can imagine that starting containers is very fast and has a very low footprint on the host.

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 Remove the containers

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docker container ls
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docker container stop 0a8fa98d3b93
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docker system prune
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Lab 3 Orchestrate applications with Docker Swarm

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 Container orchestration

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What about production ?\nAutomated scheduling and scaling, zero downtime deployments, high availability and fault tolerance…

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What is container orchestration ?

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Docker swarm, Kubernetes, …\nWith hosted solutions :

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Setup a 3 node cluster with container orchestration with Docker Swarm.

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 Create your first swarm

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Using https://labs.play-with-docker.com/\nCreate a new instance

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docker swarm init --advertise-addr eth0
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To add a worker in this swarm :

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docker swarm join --token SWMTKN-1-61p9nb8opn3tg8lchklkbyjz7uhysj8krjexrlaxpr3kaprte8-ex2t37ry9f8ux0xu92u3jfsm8 192.168.0.8:2377
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To add a manager :

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docker swarm join-token manager
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You can think of Docker Swarm as a special mode that is activated by the command: docker swarm init. The —advertise-addr option specifies the address in which the other nodes will use to join the swarm.

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With other instances, you can join the swarm by running

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docker swarm join --token SWMTKN-1-61p9nb8opn3tg8lchklkbyjz7uhysj8krjexrlaxpr3kaprte8-ex2t37ry9f8ux0xu92u3jfsm8 192.168.0.8:2377
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Back on node1, run

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docker node ls
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 Deploy your first service

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To run containers on a Docker Swarm, you need to create a service. A service is an abstraction that represents multiple containers of the same image deployed across a distributed cluster.

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The —mount flag is useful to have NGINX print out the hostname of the node it’s running on. You will use this later in this lab when you start load balancing between multiple containers of NGINX that are distributed across different nodes in the cluster and you want to see which node in the swarm is serving the request.

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docker service ls
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docker service ps nginx1
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Scale your service

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Update your service with an updated number of replicas.

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docker service update --replicas=5 --detach=true nginx1\nnginx1
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docker service ps nginx1
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docker service logs nginx1
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Apply rolling updates

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docker service update --image nginx:1.13 --detach=true nginx1
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Reconcile problems with containers

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docker swarm leave
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 Determine how many nodes you need

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For a production application, you should provision a cluster with multiple manager nodes to allow for manager node failiures.\nAt least 3 manager nodes, but no more than 7.

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Play with docker Templates :\n\n \n \n \n \n

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Summary

\n","frontmatter":{"title":"Docker training","date":"March 13, 2020","description":"Notes taken during Docker training"}}},"pageContext":{"slug":"/docker-training/","previous":{"fields":{"slug":"/lambda-training/"},"frontmatter":{"title":"Lambda training","tags":["training","AWS"]}},"next":{"fields":{"slug":"/karbon/karbon/"},"frontmatter":{"title":"Karbon Editor","tags":["article","react"]}}}},"staticQueryHashes":["2841359383","3145232782"]}