Connection fails when DOCKER_HOST set to local socket

[dsyer]

Running mvn spring-boot:build-image and getting this error:

...
[ERROR] Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:2.3.0.M4:build-image (default-cli) on project 
demo: Execution default-cli of goal org.springframework.boot:spring-boot-maven-plugin:2.3.0.M4:build-image failed: Docker API c
all to '/var/run/docker/docker.sock/v1.24/images/create?fromImage=docker.io%2Fcloudfoundry%2Fcnb%3Abionic-platform-api-0.2' fai
led with status code 500 "/var/run/docker/docker.sock: Name or service not known" -> [Help 1]                                  
[ERROR]                                                                                                                        
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.                                            
[ERROR] Re-run Maven using the -X switch to enable full debug logging.                                                         
[ERROR]                                                                                                                        
[ERROR] For more information about the errors and possible solutions, please read the following articles:                      
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException                                     

The Docker CLI works fine via a DOCKER_HOST env var (probably a plausible analog of a "standard" low-trust enterprise environment). I assume that this is messing with the Maven plugin.

[dsyer]

This was in eduk8s BTW, and the workshop died before I had a chance to get more details. It's a restrictive environment but probably not unrealistic in the wild.

[philwebb]

#20538 was fixed in M4 so there must be something we missed.

[dsyer]

That does look like a similar issue. In this case DOCKER_HOST was set to a socket (ie a file) so maybe that’s the corner case we didn’t cover yet?

[jorgemoralespou]

We can confirm this is still happening and as @dsyer mentions we think that it's a problem when Docker socket is not treated like a linux socket but rather as an http endpoint. We can see a stacktrace like this:

rg.springframework.boot:spring-boot-maven-plugin:2.3.0.BUILD-SNAPSHOT:build-image (default-cli) on project demo:
 Execution default-cli of goal org.springframework.boot:spring-boot-maven-plugin:2.3.0.BUILD-SNAPSHOT:build-image failed: Docker API cal
l to '/var/run/docker/docker.sock/v1.24/images/create?fromImage=gcr.io%2Fpaketo-buildpacks%2Fbuilder%3Abase-platform-api-0.3' failed wit
h status code 500 "/var/run/docker/docker.sock: Name or service not known"

This trace makes us think that connection to a socket is not being made properly.

[dsyer]

Here's the detail from the stack trace:

Caused by: org.springframework.boot.buildpack.platform.docker.transport.DockerEngineException: Docker API call to '/var/run/doc
ker/docker.sock/v1.24/images/create?fromImage=gcr.io%2Fpaketo-buildpacks%2Fbuilder%3Abase-platform-api-0.3' failed with status 
code 500 "/var/run/docker/docker.sock: Name or service not known"                                                              
    at org.springframework.boot.buildpack.platform.docker.transport.HttpClientTransport.execute (HttpClientTransport.java:140) 
    at org.springframework.boot.buildpack.platform.docker.transport.HttpClientTransport.post (HttpClientTransport.java:82)     
    at org.springframework.boot.buildpack.platform.docker.DockerApi$ImageApi.pull (DockerApi.java:155)                         
    at org.springframework.boot.buildpack.platform.build.Builder.pullBuilder (Builder.java:84)                                 
    at org.springframework.boot.buildpack.platform.build.Builder.build (Builder.java:62)                                       
    at org.springframework.boot.maven.BuildImageMojo.buildImage (BuildImageMojo.java:136)                                      
    at org.springframework.boot.maven.BuildImageMojo.execute (BuildImageMojo.java:128)                                         
...

I can confirm that the socket works with curl:

$ curl --unix-socket /var/run/docker/docker.sock http://localhost/images/json | jq                                         
[                                                                                                                              
  {                                                                                                                            
    "Containers": -1,                                                                                                          
    "Created": 1588752403,                                                                                                     
    "Id": "sha256:0f3310167bdc7dd1f27409b870b82c61f200ddac4c44aea5f456b024cc295b5d",                                           
    "Labels": null,                                                                                                            
    "ParentId": "",                                                                                                            
    "RepoDigests": [                                                                                                           
      "dsyer/demo@sha256:6477cd3f8bf2f17faafb0babef5e24b565ab6fa6cdd35e52011beec55dafd6ca",                                    
      "lab-spring-boot-w01-s001-registry.training.failk8s.dev/springguides/demo@sha256:6477cd3f8bf2f17faafb0babef5e24b565ab6fa6
cdd35e52011beec55dafd6ca"                                                                                                      
    ],                                                                                                                         
    "RepoTags": [                                                                                                              
      "dsyer/demo:latest",                                                                                                     
      "lab-spring-boot-w01-s001-registry.training.failk8s.dev/springguides/demo:latest"                                        
    ],                                                                                                                         
    "SharedSize": -1,                                                                                                          
    "Size": 123002083,                                                                                                         
    "VirtualSize": 123002083                                                                                                   
  }                                                                                                                            
]  

[scottfrederick]

Docker socket is not treated like a linux socket but rather as an http endpoint.

Currently, when the DOCKER_HOST environment variable is set Spring Boot assumes that it is an HTTP endpoint. If DOCKER_HOST is not set then Boot uses a domain socket on Linux. We'll need to update this logic to handle this case where DOCKER_HOST is a domain socket.