Chapter 2. .NET Core 2.0 on Red Hat OpenShift Container Platform

2.1. Install Image Streams

  1. The image stream definitions may already be part of your OpenShift Container Platform installation. Run the following command to list all dotnet versions that are available globally.

    $ oc describe is dotnet --namespace openshift
  2. If the 2.0 release is not part of the output, you can add the image streams to your installation. The image streams can be added to the current project.

    $ oc create -f https://raw.githubusercontent.com/redhat-developer/s2i-dotnetcore/master/dotnet_imagestreams.json
  3. You can also add the image streams globally if you have sufficient rights.

    $ oc create --namespace openshift -f https://raw.githubusercontent.com/redhat-developer/s2i-dotnetcore/master/dotnet_imagestreams.json

2.2. Deploy Applications

  1. Run the following commands to deploy the ASP.NET Core application, which is in the app folder on the dotnetcore-2.0 branch of the redhat-developer/s2i-dotnetcore-ex GitHub repository.

    $ oc new-app --name=exampleapp dotnet:2.0~https://github.com/redhat-developer/s2i-dotnetcore-ex#dotnetcore-2.0 --build-env DOTNET_STARTUP_PROJECT=app
  2. As suggested by the output of the new-app command, you can track progress of the build using the oc logs command.

    $ oc logs -f bc/exampleapp
  3. Once the build is finished, you can see the deployed application.

    $ oc logs -f dc/exampleapp
  4. At this point, the application is accessible within the project. To make it accessible externally, use the oc expose command. You can then use oc get routes to find the URL.

    $ oc expose svc/exampleapp
    $ oc get routes

2.3. Configuration

The .NET Core images support a number of environment variables to control the build behavior of your .NET Core application. These variables can be set as part of the build configuration, or they can be added to an .s2i/environment file in the application source code repository.

Variable NameDescriptionDefault

DOTNET_STARTUP_PROJECT

Used to select the project to run. This must be a project file (for example, csproj or fsproj) or a folder containing a single project file.

 

DOTNET_ASSEMBLY_NAME

Used to select the assembly to run. This must not include the .dll extension. Set this to the output assembly name specified in csproj (PropertyGroup/AssemblyName).

The name of the csproj file

DOTNET_RESTORE_SOURCES

Used to specify the space-separated list of NuGet package sources used during the restore operation. This overrides all of the sources specified in the NuGet.config file.

Unset

DOTNET_NPM_TOOLS

Used to specify a list of NPM packages to install before building the application.

Unset

DOTNET_TEST_PROJECTS

Used to specify the list of test projects to test. This must be project files or folders containing a single project file. dotnet test is invoked for each item.

Unset

DOTNET_CONFIGURATION

Used to run the application in Debug or Release mode. This value should be either Release or Debug.

Release

ASPNETCORE_URLS

This variable is set to http://*:8080 to configure ASP.NET Core to use the port exposed by the image. Changing this is not recommended.

http://*:8080

2.4. Sample Applications

Three sample applications are available:

  • dotnet-example: This is the default model–view–controller (MVC) application.
  • dotnet-runtime-example: This shows how to build an MVC application using a chained build and the .NET runtime image.
  • dotnet-pgsql-persistent: This is the Microsoft ASP.NET Core MusicStore sample application using a PostgreSQL backend.

To add the samples using the OpenShift Web Console, browse to your project and click Add to project. You can filter for dotnet. If the samples do not show up, you can add them to your installation by running the following commands.

$ oc create -f https://raw.githubusercontent.com/redhat-developer/s2i-dotnetcore/master/templates/dotnet-example.json
$ oc create -f https://raw.githubusercontent.com/redhat-developer/s2i-dotnetcore/master/templates/dotnet-runtime-example.json
$ oc create -f https://raw.githubusercontent.com/redhat-developer/s2i-dotnetcore/master/templates/dotnet-pgsql-persistent.json

2.5. Create a Runtime Image

The .NET Core runtime image contains the files sufficient to run a .NET application, but not to build one. As such, you must provide an already published application for the runtime image. This can be a static application inside of an image that layers on top of the runtime image or a new image can be built that is fed the application from a build image. This last method is commonly referred to as chaining builds.

Deploying a build chain requires a more in-depth configuration than a simple application build. At a minimum, a build chain needs:

  • a build config for the build image
  • a build config for the runtime image
  • an inline dockerfile for the runtime image
  • a deployment config that uses the runtime image

The following elements are optional but recommended:

  • an internal image stream
  • a trigger for the build image based on the source project
  • a trigger for the runtime build based on the build image

See dotnet-runtime-example template for an example of such a configuration.

In this template, we define a *-build and a *-runtime build config. The build image builds from a GitHub project and has a trigger to rebuild automatically when the project changes or when the base image (in this case, dotnet-20-rhel7) updates.

The runtime image builds from the dotnet-20-runtime-rhel7 base image but pulls a tar.gz file from the build image that contains the build project. That is done using this source definition in the build config.

"source": {
    "dockerfile": "FROM ${DOTNET_RUNTIME_IMAGE_STREAM_TAG}\nADD app.tar.gz .",
    "images": [
        {
            "from": {
                "kind": "ImageStreamTag",
                "name": "${NAME}-build:latest"
            },
            "paths": [
                {
                    "sourcePath": "/opt/app-root/app.tar.gz",
                    "destinationDir": "."
                }
            ]
        }
    ]
}

The runtime image also has triggers to rebuild automatically when build image is updated in the projects internal image stream or when the dotnet-20-runtime-rhel7 base image updates.

There is also a deployment defined for the runtime image. A deployment is not necessary for the build image.

The use of these triggers means that any object in the chain will be rebuilt as necessary when images or code is updated.

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