Implemented background dhparam generation

generate-dhparam.sh

@@ -0,0 +1,42 @@
+#!/bin/bash -e
+
+# If a dhparam file is not available, use the pre-generated one and generate a new one in the background.
+# Note that /etc/nginx/dhparam is a volume, so this dhparam will persist restarts.
+PREGEN_DHPARAM_FILE="/app/dhparam.pem.default"
+DHPARAM_FILE="/etc/nginx/dhparam/dhparam.pem"
+DHPARAM_BITS="2048"
+GEN_LOCKFILE="/tmp/dhparam_generating.lock"
+
+# The hash of the pregenerated dhparam file is used to check if the pregen dhparam is already in use
+PREGEN_HASH=$(md5sum $PREGEN_DHPARAM_FILE | cut -d" " -f1)
+if [[ -f $DHPARAM_FILE ]]; then
+    CURRENT_HASH=$(md5sum $DHPARAM_FILE | cut -d" " -f1)
+    if [[ $PREGEN_HASH != $CURRENT_HASH ]]; then
+        # There is already a dhparam, and it's not the default
+        exit 0
+    fi
+
+    if [[ -f $GEN_LOCKFILE ]]; then
+        # Generation is already in progress
+        exit 0
+    fi
+fi
+
+cat >&2 <<-EOT
+WARNING: $DHPARAM_FILE was not found. A pregenerated dhparam.pem will be used for now while a new one
+is being generated in the background.  Once the new dhparam.pem is in place, nginx will be reloaded.
+EOT
+
+# Put the default dhparam file in place so we can start immediately
+cp $PREGEN_DHPARAM_FILE $DHPARAM_FILE
+touch $GEN_LOCKFILE
+
+# Generate a new dhparam in the background in a low priority and reload nginx when finished (grep removes the progress indicator).
+(
+    (
+        nice -n +5 openssl dhparam -out $DHPARAM_FILE $DHPARAM_BITS 2>&1 \
+        && echo "dhparam generation complete, reloading nginx" \
+        && nginx -s reload
+    ) | grep -vE '^[\.+]+'
+    rm $GEN_LOCKFILE
+) &