We are seeing what I would like to describe as a bug in AppStream, allthoug the expected behaviour is just based on intuition, and not really documented.

Problem Description

When running the start script in AppStream, the environment variable APPSTREAM_SESSION_CONTEXT contains the session-context specified for the previous session (same user, same fleet), not the current session.

If I for example run (Session #1)

aws appstream create-streaming-url --stack-name my-stack --fleet-name my-fleet --user-id 10 --application-id notepad --session-context CONTEXT-A

And have a start script including this line:

Write-Output "CONTEXT=$($env:APPSTREAM_SESSION_CONTEXT)"

It will print

CONTEXT=

Now, if I expire that session and start a new (Session #2) using

aws appstream create-streaming-url --stack-name my-stack --fleet-name my-fleet --user-id 10 --application-id notepad --session-context CONTEXT-B

It will print (with an A and not the expected B)

CONTEXT=CONTEXT-A

This is only the case in the shell of the start script, not in a shell later opened by the user. In a shell opened by the user, the "correct" (the specified) context is set. That is, in the Session #1$env:APPSTREAM_SESSION_CONTEXT=CONTEXT-A and in the Session #2 $env:APPSTREAM_SESSION_CONTEXT=CONTEXT-B.

My setup

I connect to the AppStream instance using a Browser.

Start script

Setup:

With start script I mean the executable specified in SessionStart of the config.json file:

{
  "SessionStart": {
    "executables": [
      {
        "context": "user",
        "filename": "C:\\Windows\\system32\\WindowsPowerShell\\v1.0\\powershell.exe",
        "arguments": "-NonInteractive -File C:\\Scripts\\start_script.ps1",
        "s3LogEnabled": true
      }
    ],
    "waitingTime": 60
  }
}

Start script itself (Powershell)

$StartDate = (Get-Date).ToUniversalTime()
$AppStreamImgArn = $env:AppStream_Image_Arn
$SessionID = (Get-Item Env:AppStream_Session_ID).Value
$AS2UserName = (Get-Item Env:AppStream_UserName).Value
$AS2StackName = (Get-Item Env:AppStream_Stack_Name).Value
$AS2FleetName = (Get-Item Env:AppStream_Resource_Name).Value

Write-Output "User $AS2UserName starting session $SessionID in $AS2StackName/$AS2FleetName at $((Get-Date).ToUniversalTime())"
Write-Output "ImageArn: $AppStreamImgArn"
Write-Output "CONTEXT=$($env:APPSTREAM_SESSION_CONTEXT)"

Stack

  MyStack:
    Type: AWS::AppStream::Stack
    Properties:
      Name: my-stack
      StorageConnectors:
        - ConnectorType: 'HOMEFOLDERS'
          ResourceIdentifier: 'MyIdentifier'
      ApplicationSettings:
        Enabled: true
        SettingsGroup: AStack
      EmbedHostDomains:
        - !Ref EmbedHostDomain
      RedirectURL: !Ref RedirectURL

Fleet

  MyFleet:
    Type: AWS::AppStream::Fleet
    Properties:
      Name: my-fleet
      DisplayName: My Fleet
      InstanceType: stream.graphics-design.large
      FleetType: ON_DEMAND
      StreamView: APP
      ComputeCapacity:
        DesiredInstances: 1
      VpcConfig:
        SubnetIds: !ImportValue
              'Fn::Sub': '${NetworkStackName}-PrivateSubnet1'
        SecurityGroupIds:
          - !ImportValue
            'Fn::Sub': '${NetworkStackName}-NoIngressSecurityGroup'
      MaxUserDurationInSeconds: 345600
      DisconnectTimeoutInSeconds: 7200
      IdleDisconnectTimeoutInSeconds: 0 # Disabled
      EnableDefaultInternetAccess: False
      IamRoleArn: !GetAtt AppStreamFleetRole.Arn
      ImageArn: arn:aws:appstream:eu-west-1::image/AppStream-Graphics-Design-WinServer2019-03-24-2024