Make host header correct from upstream

I configured simple load balancer scheme on the windows:

upstream app.local {
    server app1.local:8001 fail_timeout=10s max_fails=10;
    server app2.local:8002 fail_timeout=10s max_fails=10;
}

server {
    listen 8000;

    location / {
        proxy_pass http://app.local;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $remote_addr;
    }
}

Changed hosts file like this

127.0.0.1       app.local
127.0.0.1       app1.local
127.0.0.1       app2.local

All fine, but my web servers behind app1.local and app2.local receive incorrect headers Host: app.local and therefore don’t want resolve requests. I readed
the post where the same problem but top answer not resolved my and i don’t want to use the double layer proxy option straight off.