What does the DOCKER HOST variable do

Question

I m new to Docker  using Boot2Docker on OSX  After booting it  this message is given   To connect the Docker client to the Docker daemon  please set export DOCKER HOST tcp   192 168 59 103 2375   Yet even without it  basic Docker commands  eg  docker run hello-world  work fine   The install instructions aren t very informative   Note  If you see a message in the terminal that looks something like this  To connect the Docker client to the Docker daemon  please set   export  DOCKER HOST tcp   192 168 59 103 2375 you can safely set the evironment variable as instructed    Knowing that it s  safe  doesn t say why it s useful   What I m not clear on    What is the docker  client   What is the docker  daemon   What is the docker  host    The Boot2Docker VM itself

User · Answer

It points to the docker host  I followed these steps     boot2docker start  Waiting for VM and Docker daemon to start                                   Started   To connect the Docker client to the Docker daemon  please set      export DOCKER HOST tcp   192 168 59 103 2375    export DOCKER HOST tcp   192 168 59 103 2375    docker run ubuntu 14 04  bin echo  Hello world  Unable to find image  ubuntu 14 04  locally Pulling repository ubuntu 9cbaf023786c  Download complete  511136ea3c5a  Download complete  97fd97495e49  Download complete  2dcbbf65536c  Download complete  6a459d727ebb  Download complete  8f321fc43180  Download complete  03db2b23cf03  Download complete  Hello world   See  http   docs docker com userguide dockerizing

User · Answer

Ok  I think I got it   The client is the docker command installed into OS X    The host is the Boot2Docker VM   The daemon is a background service running inside Boot2Docker   This variable tells the client how to connect to the daemon   When starting Boot2Docker  the terminal window that pops up already has DOCKER HOST set  so that s why docker commands work  However  to run Docker commands in other terminal windows  you need to set this variable in those windows   Failing to set it gives a message like this     docker run hello-world 2014 08 11 11 41 42 Post http    var run docker sock v1 13 containers create   dial unix  var run docker sock  no such file or directory   One way to fix that would be to simply do this     export DOCKER HOST tcp   192 168 59 103 2375   But  as pointed out by others  it s better to do this       boot2docker shellinit    docker run hello-world Hello from Docker          To spell out this possibly non-intuitive Bash command  running boot2docker shellinit returns a set of Bash commands that set environment variables   export DOCKER HOST tcp   192 168 59 103 2376 export DOCKER CERT PATH  Users ddavison  boot2docker certs boot2docker-vm export DOCKER TLS VERIFY 1   Hence running   boot2docker shellinit  generates those commands  and then runs them

User · Answer

Upon investigation  it s also worth noting that when you want to start using docker in a new terminal window  the correct command is     boot2docker shellinit    I had tested these commands    gt  gt   docker info Get http    var run docker sock v1 15 info  dial unix  var run docker sock  no such file or directory  gt  gt   boot2docker shellinit Writing  Users ddavison  boot2docker certs boot2docker-vm ca pem Writing  Users ddavison  boot2docker certs boot2docker-vm cert pem Writing  Users ddavison  boot2docker certs boot2docker-vm key pem     export DOCKER HOST tcp   192 168 59 103 2376     export DOCKER CERT PATH  Users ddavison  boot2docker certs boot2docker-vm     export DOCKER TLS VERIFY 1  gt  gt  docker info Get http    var run docker sock v1 15 info  dial unix  var run docker sock  no such file or directory   Notice that docker info returned that same error   however   when using   boot2docker shellinit       gt  gt     boot2docker init  Writing  Users ddavison  boot2docker certs boot2docker-vm ca pem Writing  Users ddavison  boot2docker certs boot2docker-vm cert pem Writing  Users ddavison  boot2docker certs boot2docker-vm key pem  gt  gt   docker info Containers  3

[macos] What does the DOCKER_HOST variable do?

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