nginx proxy_pass 502 Bad gateway

I use proxy_pass to proxy local API requests to our dev servers, something like

proxy_pass https://dev-server.com/api

All of a sudden, it stops working with a "502 Bad Gateway" error in browser DevTool network. However I can access https://dev-server.com/api directly using web browser.

It is obvious that nginx upstream fails for some reason. I googled a lot, and most discussions are relating to nginx configuration. However, I didn't change anything to nginx configuration before it stops working. Something happened on api server side?

Yes, our api server turned off TLSv1.0 due to security concern. I checked my local nginx and openssl versions, and realized we have 2 options:
1. Upgrade openssl version
2. Rollback api server changes to allow TLSv1.0

$ /usr/local/nginx/sbin/nginx -v
nginx version: nginx/1.0.15

$ openssl version -a
OpenSSL 0.9.8zh 14 Jan 2016
built on: Jan 23 2017
platform: darwin64-x86_64-llvm
options:  bn(64,64) md2(int) rc4(ptr,char) des(idx,cisc,16,int) blowfish(idx)
compiler: -arch x86_64 -fmessage-length=0 -pipe -Wno-trigraphs -fpascal-strings -fasm-blocks -O3 -D_REENTRANT -DDSO_DLFCN -DHAVE_DLFCN_H -DL_ENDIAN -DMD32_REG_T=int -DOPENSSL_NO_IDEA -DOPENSSL_PIC -DOPENSSL_THREADS -DZLIB -mmacosx-version-min=10.6
OPENSSLDIR: "/System/Library/OpenSSL"

How to enable TLSv1.2 in Nignx?
https://askubuntu.com/questions/319192/how-to-enable-tls-1-2-in-nginx

ssl_protocols TLSv1.2 TLSv1.1 TLSv1;

ssl_ciphers ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:DHE-RSA-AES256-SHA;
ssl_prefer_server_ciphers on;