@wesleylc1
Then it seems you have answered your question why the host header must be send in checks 👍 . HAProxy's health-checks by default do not send this header and your nginx configuration needs it to find the correct virtual host with the server_name configuration. The 'default virtual host' likely returns the 400 response status. Its nice to know that doing some research and actually understanding how things work you can succeed with fishing without needing other people to give you the fish, that will definitely help with future diagnosing of issues.
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