The correct option is Mount an Azure Files share from the target storage account as a volume into the container instance during creation.

Azure Container Instances support mounting Azure Files shares as volumes when you create the container group. Mounting an Azure Files share provides persistent file storage that is mounted into the container filesystem and remains available across restarts. To set this up you specify the file share and supply the storage account credentials or a SAS token at creation time so the share is mounted for the container.

Provide the storage account connection string as an environment variable when creating the container instance is incorrect because handing the connection string to the container does not create a filesystem mount. The application would need to use that string and implement file I O or SDK calls and this approach exposes credentials in the environment rather than providing a mounted persistent volume.

Set the restart policy to Always and pass the storage account connection string as a command line argument when launching the container instance is incorrect because the restart policy only controls container lifecycle behavior and does not provision persistent storage. Passing the connection string on the command line also does not mount a share and it exposes credentials in a non persistent way.

Assign a system assigned managed identity to the container instance and grant it a Data Storage role on the storage account so the container can authenticate without keys is incorrect for mounting Azure Files in ACI. Managed identities can let the container call Azure APIs or obtain tokens for programmatic access, but ACI does not use a managed identity to perform the SMB mount of an Azure Files share at creation time. In practice you must still provide mount credentials or a SAS token when creating the volume, or access storage programmatically from inside the container using the identity.

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