Introduction

Currently, in order to run Sitecore in docker locally, one has to pull the code from a GitHub repository, build it (if not done yet, or pull already built images from a Docker registry), set the license file, and say "up" to docker-compose. Not to say the prerequisites required. If dealing with a cloud, then the deployment into Kubernetes is required, which also demands adequate skills.

Imagine an ideal situation where you don't need to do all the things, but just pull a "managing" image from a remote registry, and this image itself will care about running "all the things" internally, such as prerequisites, pulling the dependent images, preparing the environments, network and dependencies, doing alternative steps to docker-compose and much more.

Or going far beyond that: shipping is as a traditional GUI installer for non-technical people or deploying that same image into a cloud, any cloud, ready to use, does not that look as such desirable? What if I tell you this technology is already available and you can use it? Please welcome the new universal spec for packaging distributed apps created by Microsoft and Docker:

Cloud-Native Application Bundles or simply CNAB

Firstly, what the heck is CNAB at all? Using Cloud Native Application Bundle, a developer has an option of deploying the app either locally at his dev. machine, or in a public cloud as it bolts together containers and services into a seamless whole, placing a strong focus on standardization. It is an open-source specification that aims to facilitate the bundling, installing, and managing of containerized apps. With this bundle, users can define resources that can then be deployed to a number of run-time environments, such as Docker, Azure, Kubernetes, Helm, automation services (such as those used by GitOps), and more.

At a first glance, that task is supposed to be solved by Docker itself. However, when dealing with largely scaled hybrid infrastructures, its standard features become insufficient. Thus, CNAB is an attempt of standardizing the process of packaging, deployment, and lifecycle management of distributed apps on a basis of Kubernetes, Helm, Swarm, and others by using a unified JSON-based package format. 

Tooling

And of course, Docker App is a CNAB builder and installer that leverages the Docker Compose format to define your applications. To facilitate developer-to-operator handover, you can add metadata and run-time parameters. These applications can easily be shared using existing container registries. Docker App is available as part of the latest Docker release.

{ 
   "credentials":{ 
      "hostkey":{ 
         "env":"HOST_KEY",
         "path":"/etc/hostkey.txt"
      }
   },
   "custom":{ 
      "com.example.backup-preferences":{ 
         "frequency":"daily"
      },
      "com.example.duffle-bag":{ 
         "icon":"https://example.com/icon.png",
         "iconType":"PNG"
      }
   },
   "definitions":{ 
      "http_port":{ 
         "default":80,
         "maximum":10240,
         "minimum":10,
         "type":"integer"
      },
      "port":{ 
         "maximum":65535,
         "minimum":1024,
         "type":"integer"
      },
      "string":{ 
         "type":"string"
      },
      "x509Certificate":{ 
         "contentEncoding":"base64",
         "contentMediaType":"application/x-x509-user-cert",
         "type":"string",
         "writeOnly":true
      }
   },
   "description":"An example 'thin' helloworld Cloud-Native Application Bundle",
   "images":{ 
      "my-microservice":{ 
         "contentDigest":"sha256:aaaaaaaaaaaa...",
         "description":"my microservice",
         "image":"example/microservice:1.2.3"
      }
   },
   "invocationImages":[ 
      { 
         "contentDigest":"sha256:aaaaaaa...",
         "image":"example/helloworld:0.1.0",
         "imageType":"docker"
      }
   ],
   "maintainers":[ 
      { 
         "email":"matt.butcher@microsoft.com",
         "name":"Matt Butcher",
         "url":"https://example.com"
      }
   ],
   "name":"helloworld",
   "outputs":{ 
      "clientCert":{ 
         "definition":"x509Certificate",
         "path":"/cnab/app/outputs/clientCert"
      },
      "hostName":{ 
         "applyTo":[ 
            "install"
         ],
         "definition":"string",
         "description":"the hostname produced installing the bundle",
         "path":"/cnab/app/outputs/hostname"
      },
      "port":{ 
         "definition":"port",
         "path":"/cnab/app/outputs/port"
      }
   },
   "parameters":{ 
      "backend_port":{ 
         "definition":"http_port",
         "description":"The port that the back-end will listen on",
         "destination":{ 
            "env":"BACKEND_PORT"
         }
      }
   },
   "schemaVersion":"v1.0.0",
   "version":"0.1.2"
}