Add nsswitch.conf also for alpine

alpine/Dockerfile

@@ -11,6 +11,7 @@ RUN set -ex; \
 	wget --quiet -O /usr/local/bin/traefik "https://github.com/containous/traefik/releases/download/v1.7.4/traefik_linux-$arch"; \
 	chmod +x /usr/local/bin/traefik
 COPY entrypoint.sh /
+COPY /etc/nsswitch.conf /etc/
 EXPOSE 80
 ENTRYPOINT ["/entrypoint.sh"]
 CMD ["traefik"]

alpine/etc/nsswitch.conf

@@ -0,0 +1,20 @@
+# /etc/nsswitch.conf
+#
+# Example configuration of GNU Name Service Switch functionality.
+# If you have the `glibc-doc-reference' and `info' packages installed, try:
+# `info libc "Name Service Switch"' for information about this file.
+
+passwd:         compat
+group:          compat
+shadow:         compat
+gshadow:        files
+
+hosts:          files dns
+networks:       files
+
+protocols:      db files
+services:       db files
+ethers:         db files
+rpc:            db files
+
+netgroup:       nis