Ugh. envsubst doesn't do exact string match. Throw in extra slash, then remove it afterward. UGH.

Dockerfile

@@ -27,8 +27,7 @@ RUN chmod +x ./entrypoint.sh
 # Substitute environment variables in nginx configuration and index.html
 ENTRYPOINT ["./entrypoint.sh", \
             "/usr/share/nginx/html/index.html,/etc/nginx/conf.d/default.conf", \
-            "PRODUCTION,API_URL,IRB_URL,HOME_ROUTE,BASE_HREF,PORT0", \
+            "PRODUCTION,API_URL,IRB_URL,HOME_ROUTE,BASE_HREF,PORT0"]
-            "/usr/share/nginx/html/index.html"]
 
 ### STAGE 3: Profit! ###
 CMD ["nginx", "-g", "daemon off;"]

docker/substitute-env-variables.sh

@@ -5,7 +5,6 @@
 # Parameters:
 # $1: Comma-delimited list of file paths
 # $2: Comma-delimited list of environment variables
-# $3: File path to index.html (optional)
 #####################################################################
 
 echo 'Substituting environment variables...'
@@ -26,7 +25,7 @@ fi
 if [[ "$2" == *"BASE_HREF"* ]]; then
   length=${#BASE_HREF}
   last_char=${BASE_HREF:length-1:1}
-  [[ $last_char != "/" ]] && BASE_HREF="$BASE_HREF/"; :
+  [[ $last_char == "/" ]] && BASE_HREF="$BASE_HREF"; :
 fi
 
 # Convert "VAR1,VAR2,VAR3,..." to "\$VAR1 \$VAR2 \$VAR3 ..."
@@ -39,6 +38,19 @@ do
   envsubst "$env_list" < "$file_path" > "$file_path".tmp && mv "$file_path".tmp "$file_path"
 
   echo '...'
+  #  Wait a second in case envsubst needs more time
+  sleep 1
+
+  # If this is the index.html file, rewrite base href.
+  # Use @ as a sed delimiter because $BASE_HREF will contain a / character
+  if [[ $file_path == *"/index.html"* ]]; then
+    sed -i -e 's@<base href\=\"\/\">@<base href\=\"'"$BASE_HREF"'\">@' "$3"
+  fi
+
+  # If this is the nginx default.conf file, replace double slashes with single slashes
+  if [[ $file_path == *"/default.conf"* ]]; then
+    sed -i -e 's@//@/@g' "$file_path"
+  fi
 done
 
 echo 'Finished substituting environment variables.'
@@ -47,19 +59,5 @@ do
   echo "$env_var = ${!env_var}"
 done
 
-# The third parameter is the path to the index.html file
+# Execute all other commands with parameters
-# Rewrite base href in index.html.
+exec "${@:3}"
-# Use @ as a sed delimiter because $BASE_HREF will contain a / character
-if [[ -z $3 ]]; then
-  # Execute all other commands with parameters
-  exit 0
-else
-  #  Wait a second in case envsubst needs more time
-  sleep 1
-  sed -i -e 's@<base href\=\"\/\">@<base href\=\"'"$BASE_HREF"'\">@' "$3"
-
-  # Execute all other commands with parameters
-  exec "${@:4}"
-fi
-
-

nginx.conf

@@ -3,9 +3,9 @@ server {
   root /usr/share/nginx/html;
   index index.html index.htm;
 
-  location $BASE_HREF {
+  location $BASE_HREF/ {
     alias /usr/share/nginx/html;
-    try_files $uri$args $uri$args/ $BASE_HREFindex.html =404;
+    try_files $uri$args $uri$args/ $BASE_HREF/index.html =404;
   }
 
   include /etc/nginx/extra-conf.d/*.conf;