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How To Troubleshoot Docker - Best Practices ?


In this post, we will explore - How To Troubleshoot Docker Applications - Best Practices. We present below some of the step by step process to manage Docker applications that will negate any possible issues.  

  • To use Docker Desktop, your machine must have the following features -
    • WSL 2 and Windows Home
    • Virtual Machine Platform
    • Windows Subsystem for Linux
    • Virtualization enabled in the BIOS
    • Hypervisor enabled at Windows startup
    • WSL 2 enabled
  • Docker Desktop requires Hyper-V as well as the Hyper-V Module for Windows Powershell to be installed and enabled
  • Docker Desktop also needs two CPU hardware features to use Hyper-V: Virtualization and Second Level Address Translation (SLAT)
 

Volumes & Volume Mounting :

  • When sharing files from Windows, Docker Desktop sets the default permissions on shared volumes to 0777 (read, write, execute permissions for user and group)
  • These permissions are not configurable, so you may need to use non-host-mounted volumes or find a way to make your applications work with the default permissions if they require different permissions at runtime
  • Volume mounting requires shared folders for Linux containers
  • If you encounter runtime errors related to volume mounts,
    • such as file not found,
    • access denied, or
    • service unable to start,
you may need to enable shared folders

  • To enable shared folders, go to the Settings tab and select Shared Folders, then share the folder that contains the Dockerfile and volume Note: With the Hyper-V backend, mounting files from Windows requires shared folders for Linux containers
 

  • Use Unix style \n line endings for files in containers
  • This includes files referenced at the command line for builds and in RUN commands in Docker files
  • Docker containers and docker build run in a Unix environment, so files must use Unix style line endings
  • Windows style \r\n line endings will cause syntax errors when running in a Unix-based container
  • To avoid this issue, use Unix style line endings or convert Windows style line endings to Unix style when authoring files in Windows tools
 

Directory Paths :

  • On Linux, the system automatically mounts a path to another path when using the -v flag in the docker run command
  • On Windows, you must update the source path to use the appropriate format for Windows
  • You can use either a Windows-style path or a Unix-style path, but you must specify the correct format for Docker Desktop to correctly mount the directory
    • For example, to use a Windows-style path:

docker run --rm -ti -v C:\\Users\\Alex\\work:/work alpine
    • To use a Unix-style path:

docker run --rm -ti -v /c/Users/Alex/work:/work alpine ls /work
  • Docker Desktop also allows you to use Unix-style path to the appropriate format. For example:

docker run --rm -ti -v /c/Users/Alex/work:/work alpine ls /work
 

Certificates for Docker:

To ensure that Docker is correctly using certificates for secure communication with registries, you will need to follow certain process. By following these steps, it is ensured that Docker is correctly using certificates for secure communication with registries.

  • Make sure that your certificates are stored in the correct location on your system. On most systems, the recommended location for certificates is /etc/ssl/certs.
  • If you are using self-signed certificates, you will need to add them to your system's certificate trust store. On most systems, you can do this by copying the certificate file to /usr/local/share/ca-certificates and running the update-ca-certificates command.
  • If you are using a certificate authority (CA) to sign your certificates, make sure that the CA's root certificate is installed on your system. In Docker, you can specify the location of your certificates using the --tlscacert flag when starting the Docker daemon.
  • If you are trying to pull an image from a registry that requires client certificates, you will need to specify the location of your client certificate and private key using the --tlscert and --tlskey flags when running the docker pull command.
  • If you are trying to push an image to a registry that requires client certificates, you will need to specify the location of your client certificate and private key using the --tlscert and --tlskey flags when running the docker push command.
Not following proper Certificate setup, we can face issues as below -


Error response from daemon: Get http://141.121.403.139:5858/v2/: malformed HTTP response "\\x15\\x03\\x01\\x00\\x02\\x02"
 

File Sharing :

  • When using volume mounting, you may need to enable file sharing for directories outside of the $HOME directory.
  • If you encounter runtime errors related to volume mounts, such as -
    • file not found,
    • access denied, or
    • service unable to start, you may need to enable file sharing
  • To enable file sharing,
    • go to the Settings tab and select Resources,
    • then File Sharing
    • Share the drive that contains the Dockerfile and volume
  • Volume mounting requires shared drives for projects that live outside of the /home/ directory
 

Virtualization :

  • Docker Desktop requires a CPU that supports virtualization and the Apple Hypervisor framework
  • Docker Desktop is only compatible with Mac systems that have a CPU that supports the Hypervisor framework. Most latest Macs support the Hypervisor framework.
  • Check if your Mac supports the Hypervisor framework

sysctl kern.hv\_support
    • If your Mac supports the Hypervisor framework, the command will print

kern.hv\_support: 1
    • If your Mac does not support the Hypervisor framework, the command will print

kern.hv\_support: 0
    Hope you find this helpful.  

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