Try other key servers if ha.pool.sks-keyservers.net is unreachable. Closes #1029

Dockerfile

@@ -48,14 +48,24 @@ RUN \
     # Verify nodejs authenticity
     grep ${NODE_VERSION}-${ARCHITECTURE}.tar.gz SHASUMS256.txt.asc | shasum -a 256 -c - && \
     export GNUPGHOME="$(mktemp -d)" && \
-    gpg --keyserver ha.pool.sks-keyservers.net --recv-keys 9554F04D7259F04124DE6B476D5A82AC7E37093B && \
-    gpg --keyserver ha.pool.sks-keyservers.net --recv-keys 94AE36675C464D64BAFA68DD7434390BDBE9B9C5 && \
-    gpg --keyserver ha.pool.sks-keyservers.net --recv-keys FD3A5288F042B6850C66B31F09FE44734EB7990E && \
-    gpg --keyserver ha.pool.sks-keyservers.net --recv-keys 71DCFD284A79C3B38668286BC97EC7A07EDE3FC1 && \
-    gpg --keyserver ha.pool.sks-keyservers.net --recv-keys DD8F2338BAE7501E3DD5AC78C273792F7D83545D && \
-    gpg --keyserver ha.pool.sks-keyservers.net --recv-keys C4F0DFFF4E8C1A8236409D08E73BC641CC11F4C8 && \
-    gpg --keyserver ha.pool.sks-keyservers.net --recv-keys B9AE9905FFD7803F25714661B63B535A4C206CA9 && \
-    gpg --refresh-keys ha.pool.sks-keyservers.net && \
+
+    # Try other key servers if ha.pool.sks-keyservers.net is unreachable
+    # Code from https://github.com/chorrell/docker-node/commit/2b673e17547c34f17f24553db02beefbac98d23c
+    # gpg keys listed at https://github.com/nodejs/node#release-team
+    # and keys listed here from previous version of this Dockerfile
+    for key in \
+    9554F04D7259F04124DE6B476D5A82AC7E37093B \
+    94AE36675C464D64BAFA68DD7434390BDBE9B9C5 \
+    FD3A5288F042B6850C66B31F09FE44734EB7990E \
+    71DCFD284A79C3B38668286BC97EC7A07EDE3FC1 \
+    DD8F2338BAE7501E3DD5AC78C273792F7D83545D \
+    C4F0DFFF4E8C1A8236409D08E73BC641CC11F4C8 \
+    B9AE9905FFD7803F25714661B63B535A4C206CA9 \
+    ; do \
+    gpg --keyserver ha.pool.sks-keyservers.net --recv-keys "$key" || \
+    gpg --keyserver pgp.mit.edu --recv-keys "$key" || \
+    gpg --keyserver keyserver.pgp.com --recv-keys "$key" ; \
+    done && \
     gpg --verify SHASUMS256.txt.asc && \
     rm -R "$GNUPGHOME" SHASUMS256.txt.asc && \
     \