Using variable in nginx conf - nginx

Question

This works in my Nginx config:
# This works
proxy_pass http://GitLab-CE:9080;
... but this does not:
# does not work
set $upstream_gitlab GitLab-CE;
proxy_pass http://$upstream_gitlab:9080;
This was copied from a different working example which uses a hyphen and a different port.
# this works
set $upstream_deluge binhex-delugevpn;
proxy_pass http://$upstream_deluge:8112;
I thought perhaps something to do with the dash, but I have another config which also uses a hyphen in its name (see above) and it works. I have tried various forms of quotation which doesn't seem to help either. What could be going on here? I am at a loss. What is it about GitLab-CE that doesn't work yet binhex-delugevpn does work? Is Nginx seeing CE has some hexidecimal math?
Full context:
# make sure that your dns has a cname set for gitlab and that your gitlab container is not using a base url
server {
listen 443 ssl;
listen [::]:443 ssl;
server_name gitlab.*;
include /config/nginx/ssl.conf;
client_max_body_size 0;
# enable for ldap auth, fill in ldap details in ldap.conf
#include /config/nginx/ldap.conf;
location / {
# enable the next two lines for http auth
auth_basic "Restricted";
auth_basic_user_file /config/nginx/.htpasswd;
# enable the next two lines for ldap auth
#auth_request /auth;
#error_page 401 =200 /login;
include /config/nginx/proxy.conf;
resolver 127.0.0.11 valid=30s;
set $upstream_gitlab GitLab-CE;
proxy_pass http://$upstream_gitlab:9080;
}
}
I should note that 127.0.0.11 is indeed the correct resolver and the names GitLab-CE and binhex-delugevpn do correctly resolve.
Of course there is no need to use a variable when it is only being referenced a single time but this follows the templates from linuxserver.io's letsencrypt Docker image.
EDIT: more context
Here is /config/nginx/nginx.conf.
It is unmodified by me.
## Version 2018/01/29 - Changelog: https://github.com/linuxserver/docker-letsencrypt/commits/master/root/defaults/nginx.conf
user abc;
worker_processes 4;
pid /run/nginx.pid;
include /etc/nginx/modules/*.conf;
events {
worker_connections 768;
# multi_accept on;
}
http {
##
# Basic Settings
##
sendfile on;
tcp_nopush on;
tcp_nodelay on;
keepalive_timeout 65;
types_hash_max_size 2048;
# server_tokens off;
# server_names_hash_bucket_size 64;
# server_name_in_redirect off;
client_max_body_size 0;
include /etc/nginx/mime.types;
default_type application/octet-stream;
##
# Logging Settings
##
access_log /config/log/nginx/access.log;
error_log /config/log/nginx/error.log;
##
# Gzip Settings
##
gzip on;
gzip_disable "msie6";
# gzip_vary on;
# gzip_proxied any;
# gzip_comp_level 6;
# gzip_buffers 16 8k;
# gzip_http_version 1.1;
# gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;
##
# nginx-naxsi config
##
# Uncomment it if you installed nginx-naxsi
##
#include /etc/nginx/naxsi_core.rules;
##
# nginx-passenger config
##
# Uncomment it if you installed nginx-passenger
##
#passenger_root /usr;
#passenger_ruby /usr/bin/ruby;
##
# Virtual Host Configs
##
include /etc/nginx/conf.d/*.conf;
include /config/nginx/site-confs/*;
}
#mail {
# # See sample authentication script at:
# # http://wiki.nginx.org/ImapAuthenticateWithApachePhpScript
#
# # auth_http localhost/auth.php;
# # pop3_capabilities "TOP" "USER";
# # imap_capabilities "IMAP4rev1" "UIDPLUS";
#
# server {
# listen localhost:110;
# protocol pop3;
# proxy on;
# }
#
# server {
# listen localhost:143;
# protocol imap;
# proxy on;
# }
#}
daemon off;
EDIT 2:
I have verified that Nginx seems to be doing some "tolower" conversion when using variables.
I renamed my GitLab container to gitlab-ce and it worked fine.
I renamed my deluge container (and made appropriate edits to the .conf) to binhex-deLugevpn and it stopped working.
Then I renamed it back to binhex-deluge but in the .conf file I put set $upstream_deluge bInHeX-dElUgEvPn;
And it worked. So, nginx (1.14.2) from linuxserver/letsencrypt seems to be doing some lower conversions on variables.
I tried looking find /config -type f -print0 | xargs -0 grep -i lower and found nothing.