nick-brown/docker.md

## docker.md

      
    Raw
  

              docker.md
            
          
    Basics


engine/server (daemon)

docker version or docker info


Image: application we want to run

hub.docker.com (default image registry)


Container: the instance of that image running as a process

many containers can run off of the same image


docker container run --publish 80:80 --detach nginx:1.11

--publish or -p
detach runs in the background (or -d)
80:80 maps container port 80 to localhost port 80
:1.11 specifies a version but defaults to latest if not specified

docker container ls or docker ps will list running containers
docker container logs <name> will spit out logs for detached container
docker container top
docker container rm <name1> <name2> optional -f flag to remove a container that is currently running
What happens in docker container run?


looks for image locally first, then to default registry
creates new container based on that image

NOTE: the powerful part of docker is that it's not cloning the image and starting a new one, it's simply creating a new layer of changes on top of the existing image so there is no duplication


gives a virtual IP on a private network inside the docker engine
opens up port 80 and forwards to port 80 in the container
starts the container by using the CMD in the image Dockerfile

Containers aren't mini vms


just (restricted) processes
limited to what resources they can access
exit when the process stops
can see the process running on the host machine (ps aux | grep <name>)

Environment var passing


when running mysql use the --env or -e option to pass in MYSQL_RANDOM_ROOT_PASSWORD=yes

docker image ls to show all local images
Seeing what's going on inside of containers


docker container top - process list in a single container
docker container inspect - details of one container config
docker container stats or docker stats - all container streaming stats

Shell inside containers


docker container run -it - start a new container interactively (t is a pseudo-tty and i is interactive)

docker container run -it --name proxy nginx bash

normally containers will immediately run the command of the process they're starting (such as nginx) but in this case the command that was run is bash, which can be seen by looking at docker container ls -a
when you exit the shell the container stops because the startup command stopped


NOTE: mutually exclusive with --detach/-d
in the case of an image like ubuntu, bash is its default startup command

distros will have be a very minimal install


to reconnect to a stopped interactive container pass -ai (attach)

docker container start -ai ubuntu


docker container exec -it - run additional command in existing container

this will allow you to run a shell inside of an existing container, like mysql
docker exec -it <name> <new_command>
docker exec -it mysql bash
docker exec -u root -it <container_name> <new_command>


Image Management


docker pull <image_name> - fetches the image
docker image ls - show all locally cached images

Docker Network Concepts


docker container run -p - exposes default ports on the physical network


docker container port <name> - check ports


Each container connected to a private virtual network called "bridge"


each virtual network routes through the NAT firewall on host IP (docker daemon configuring the firewall on the host inferface so the containers can get out to the internet)


All containers on a virtual network can talk to each other without exposing ports with -p

Best practice here is to have a separate virtual network for each app

app1 for mysql, php, and apache
app2 for mongo and nodejs containers


containers can be connected to zero or more virtual networks


skip virtual networks and use host IP (--net=host)


can use different Docker network drivers to gain new abilities


docker container inspect --format '{{ .NetworkSettings.IPAddress }}' nginx

easier then grep when you learn the format of the container files
get the actual IP of the container
172.17.0.4 which is a different subnet than local

ifconfig en0 shows me the host is a 192.168 subnet


can also be used on services


docker network create my_app_net - creates a new virtual network to attach containers to


CLI Management


docker network ls - list networks
docker network inspect
docker network create --driver
docker network connect - attach a network to a container
docker network disconnect - detach a network from a container

Accessing container files


sudo docker cp <container_name>:/etc/nginx/nginx.conf ./ copies the /etc/nginx/nginx.conf file in the container to the current directory on the host machine
`docker container run --name nginx

Data Storage


Volumes: make special location outside of a container's unified file system

VOLUME /var/lib/mysql
stored in /var/lib/docker/volumes on the host (in a VM on Mac and Windows) and bound to /var/lib/mysql in the container
docker volume ls
needs to be destroyed separately from the container (for insurance)

docker volume prune


can name volumes with docker run -d --name mysql -v mysql-db:/var/lib/mysql:ro mysql

:ro makes it read-only


Bind Mounts: link container path to host path

can't use in Dockerfile, must be at container run
docker container run -d --name mysql -v /Users/nickbrown/data:/var/lib/mysql


Docker Compose


configures relationships between containers
save docker container run settings in file
made up of two separate but related things

yaml file describing options for containers/networks/volumes
a cli tool (docker-compose) used for local dev/test automation along with the yaml files


docker-compose up to execute the docker-compose.yaml in the current directory

  version: '3.1'  # if no version is specificed then v1 is assumed. Recommend v2 minimum

  services:  # containers. same as docker run
    site-flask-app: # a friendly name. this is also DNS name inside network
      # image: flask-app # use a pre-built image
      build: ./ # build the image in the given directory then run
      ports:
          - '80:80'
      # command: # Optional, replace the default CMD specified by the image
      # environment: # Optional, same as -e in docker run
      # volumes: # Optional, same as -v in docker run

  # volumes: # Optional, same as docker volume create

  # networks: # Optional, same as docker network create


Docker Swarm


a set of nodes all running the same docker image


managers in a Raft consesus group and workers in a gossip network

??? what does that mean ???


docker run was concerned with managing a single image, docker service replaces run and starts a swarm with an initial manager

allows us to add replicas known as tasks to
a single service can have multiple tasks, and each one of those tasks will launch a container


if we start an nginx service and tell it to create 3 replica nodes it will create a manager node running the nginx:latest image and spin up additional images (tasks) on available nodes (that don't already have the image running) in the cluster/swarm, up to the maximum of 3


to check if swarm is running, perform a docker info | grep [sS]warm


docker swarm init

performs PKI (Public Key Infrastructure)

root signing certificate created for the new swarm
certs issues for first manager node
join tokens are created (which are used to join other nodes in the swarm)


Raft database created to store root CA, configs, and secrets

Raft is a protocol used to enforce consistency across nodes in a cluster
encrypted by default on disk
prevents need for another key/value system to hold orchestration secrets (why are we using Ansible here?)

how is this provisioned within swarm?


replicates logs amongst managers via mutual TLS in the control plane


docker node ls to list nodes

there can be only one leader at a time

  ID                            HOSTNAME                STATUS              AVAILABILITY        MANAGER STATUS
  lqeiauxsuqvgah1cpj22m5g3x *   linuxkit-025000000001   Ready               Active              Leader


docker service create alpine ping 8.8.8.8 to tell the swarm to create a new task

will return a service id and assign it a random name much like containers
docker service ls to see a list of all services

  ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
  xsmfp3su05zw        nifty_dijkstra      replicated          1/1                 alpine:latest       


docker service ps nifty_dijkstra to see the actual container which will additionally tell you what node the task/container is running on

  ID                  NAME                IMAGE               NODE                    DESIRED STATE       CURRENT STATE           ERROR               PORTS
  kye1ugk97sxp        nifty_dijkstra.1    alpine:latest       linuxkit-025000000001   Running             Running 4 minutes ago                       


docker service update nifty_dijsktra --replicas 3 to scale up the cluster

another docker service ps nifty_dijsktra will show the additional tasks

  ID                  NAME                IMAGE               NODE                    DESIRED STATE       CURRENT STATE            ERROR               PORTS
  kye1ugk97sxp        nifty_dijkstra.1    alpine:latest       linuxkit-025000000001   Running             Running 6 minutes ago                        
  u59hhh38smza        nifty_dijkstra.2    alpine:latest       linuxkit-025000000001   Running             Running 29 seconds ago                       
  3d47i7q8xv1y        nifty_dijkstra.3    alpine:latest       linuxkit-025000000001   Running             Running 29 seconds ago                       


docker update will allow you to update configuration (cpu/ram/etc) of a single container, whereas service will let you control the effects across the entire swarm in a way that ensures consistent availability


docker container rm -f nifty_dijkstra.2.u59hhh38smzasaigyfsh1xkgr to remove a single task out of a swarm and docker service ls will show one removed and then shortly after that the swarm brought up a new instance

docker service ps nifty_dijsktra will show the entire history of tasks that failed and were replaced by starting a new container

  ID                  NAME                   IMAGE               NODE                    DESIRED STATE       CURRENT STATE            ERROR                         PORTS
  kye1ugk97sxp        nifty_dijkstra.1       alpine:latest       linuxkit-025000000001   Running             Running 18 minutes ago                                 
  j07xza549lkg        nifty_dijkstra.2       alpine:latest       linuxkit-025000000001   Running             Running 2 minutes ago                                  
  u59hhh38smza         \_ nifty_dijkstra.2   alpine:latest       linuxkit-025000000001   Shutdown            Failed 2 minutes ago     "task: non-zero exit (137)"   
  3d47i7q8xv1y        nifty_dijkstra.3       alpine:latest       linuxkit-025000000001   Running             Running 12 minutes ago                                 


docker service rm nifty_dijkstra to remove the entire service -- it will take a few seconds to clean up the task containers


Questions


What are the various different network drivers e.g. bridge
How are virtual network specifically different from subnets
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