Added IPv6 check script and modified nginx service to use it (fixes #2174).

.docker/localbin/check-ipv6.sh

@@ -0,0 +1,95 @@
+#!/bin/sh
+# check-ipv6-nc.sh - sh + BusyBox nc probe for AF_INET6 bind to ::
+# Exit codes:
+# 0 = IPv6 usable (nc bound to :: successfully)
+# 1 = IPv6 disabled via module/sysctl
+# 2 = nc not available or does not support required options
+# 3 = AF_INET6/socket bind not supported (bind failed)
+
+
+# helper: read file if present
+read_if_exists() {
+  if [ -r "$1" ]; then
+    cat "$1" 2>/dev/null
+  else
+    echo ""
+  fi
+}
+
+# 1) kernel/module check
+if [ -r /sys/module/ipv6/parameters/disable ]; then
+  v=$(read_if_exists /sys/module/ipv6/parameters/disable)
+  v=$(printf '%s' "$v" | tr -d '[:space:]')
+  if [ "$v" = "1" ]; then
+    printf 'IPv6 disabled: /sys/module/ipv6/parameters/disable=1\n' >&2
+    exit 1
+  fi
+fi
+
+# 1b) sysctl/global disable
+if command -v sysctl >/dev/null 2>&1; then
+  if sysctl -n net.ipv6.conf.all.disable_ipv6 >/dev/null 2>&1; then
+    v=$(sysctl -n net.ipv6.conf.all.disable_ipv6 2>/dev/null)
+    v=$(printf '%s' "$v" | tr -d '[:space:]')
+    if [ "$v" = "1" ]; then
+      printf 'IPv6 disabled: net.ipv6.conf.all.disable_ipv6=1\n' >&2
+      exit 1
+    fi
+  fi
+else
+  v=$(read_if_exists /proc/sys/net/ipv6/conf/all/disable_ipv6)
+  v=$(printf '%s' "$v" | tr -d '[:space:]')
+  if [ "$v" = "1" ]; then
+    printf 'IPv6 disabled: /proc/sys/net/ipv6/conf/all/disable_ipv6=1\n' >&2
+    exit 1
+  fi
+fi
+
+# 2) check for configured IPv6 addresses (informational)
+if [ -r /proc/net/if_inet6 ]; then
+  if [ -s /proc/net/if_inet6 ]; then
+    has_addr=1
+  else
+    has_addr=0
+  fi
+else
+  has_addr=0
+fi
+
+# 3) runtime probe using BusyBox nc
+if ! command -v nc >/dev/null 2>&1; then
+  printf 'nc not found in PATH\n' >&2
+  exit 2
+fi
+
+# Choose a random ephemeral port in 49152-65535
+now=$(date +%s 2>/dev/null || echo 0)
+port=$(( (now % 16384) + 49152 ))
+
+# Start nc listening bound to :: on chosen port, redirect output, run in background
+# Use bracketless :: for -s; BusyBox nc accepts that form.
+nc -l -s :: -p "$port" >/dev/null 2>&1 &
+pid=$!
+sleep 0.15
+
+# If process exited quickly, capture its exit status
+if ! kill -0 "$pid" >/dev/null 2>&1; then
+  # process not running; reap and inspect exit code
+  wait "$pid" 2>/dev/null
+  rc=$?
+  # Common rc: 1 for bind/address family errors; treat as AF_INET6 unsupported/bind failed
+  printf 'nc listener exited immediately with code %d\n' "$rc" >&2
+  exit 3
+fi
+
+# If still running, we succeeded in binding to ::; kill the listener and return success
+kill "$pid" >/dev/null 2>&1 || true
+# wait for it to exit to avoid zombies
+wait "$pid" 2>/dev/null || true
+
+if [ "$has_addr" -eq 1 ]; then
+  printf 'IPv6 usable: nc bound to :: succeeded; addresses present\n'
+else
+  printf 'IPv6 usable: nc bound to :: succeeded; no configured addresses found\n'
+fi
+exit 0

.docker/services.d/nginx/run

@@ -1,2 +1,13 @@
-#!/bin/execlineb -P
-nginx
+#!/bin/sh
+
+if /usr/local/bin/check-ipv6.sh; then
+  echo "IPv6 is available, starting nginx with IPv6 support"
+  exec nginx
+else
+  echo "IPv6 is not available, starting nginx without IPv6 support"
+
+  # Remove the default IPv6 listen directive from nginx.conf to avoid bind errors
+  sed -i '/^[[:space:]]*listen[[:space:]]*\[::\]:80;/d' /etc/nginx/nginx.conf
+
+  exec nginx
+fi

Dockerfile

@@ -54,6 +54,9 @@ RUN apk --no-cache del icu-data-en \
 COPY .docker/nginx.conf /etc/nginx/nginx.conf
 COPY .docker/php-fpm.conf /etc/php84/php-fpm.conf
 COPY .docker/services.d /etc/services.d
+COPY .docker/localbin/check-ipv6.sh /usr/local/bin/check-ipv6.sh
+
+RUN chmod +x /usr/local/bin/check-ipv6.sh
 
 RUN rm -rf /etc/php84/php-fpm.d/www.conf \
     && sed -i 's/post_max_size.*/post_max_size = 10M/' /etc/php84/php.ini \