SAGEMAKER_MULTI_MODE in Ping should be SAGEMAKER_MULTI_MODEL

[Michael Pham]

Per AWS documentation[1], the environment variable to decide if the container is running in Multi Model mode is SAGEMAKER_MULTI_MODEL, while in Ping.java the environment variable read is SAGEMAKER_MULTI_MODE[2]

[1] - https://docs.aws.amazon.com/sagemaker/latest/dg/build-multi-model-build-container.html

[2] -

multi-model-server/plugins/endpoints/src/main/java/software/amazon/ai/mms/plugins/endpoint/Ping.java

Line 51 in 1729efc

 String isMultiModelMode = System.getenv("SAGEMAKER_MULTI_MODE");