most important part

.env

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+NODE_MAJOR=11
+RUBY_BASE=ruby:2.6
+# node release keys pulled from https://github.com/nodejs/node#release-team
+KEYS=4ED778F539E3634C779C87C6D7062848A1AB005C 71DCFD284A79C3B38668286BC97EC7A07EDE3FC1 77984A986EBC2AA786BC0F66B01FBB92821C587A 8FCCA13FEF1D0C2E91008E09770F7A9A5AE15600 94AE36675C464D64BAFA68DD7434390BDBE9B9C5 A48C2BEE680E841632CD4E44F07496B3EB3C1762 B9AE9905FFD7803F25714661B63B535A4C206CA9 B9E2F5981AA6E0CD28160D9FF13993A75599653C C4F0DFFF4E8C1A8236409D08E73BC641CC11F4C8 DD8F2338BAE7501E3DD5AC78C273792F7D83545D FD3A5288F042B6850C66B31F09FE44734EB7990E
+TAG_VERSION=2.6-11

Dockerfile

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+ARG RUBY_BASE=ruby:2
+FROM $RUBY_BASE
+MAINTAINER [email protected]
+
+ENV LANG C.UTF-8
+
+RUN groupadd --gid 1000 node \
+  && useradd --uid 1000 --gid node --shell /bin/bash --create-home node
+
+ARG KEYS
+ENV KEYS ${KEYS}
+
+RUN mkdir ~/.gnupg
+RUN chmod 700 ~/.gnupg
+RUN echo "disable-ipv6" >> ~/.gnupg/dirmngr.conf
+
+# gpg keys listed at https://github.com/nodejs/node#release-team
+RUN set -ex \
+  && for key in ${KEYS}; \
+  do \
+    echo "$key"; \
+    gpg --no-tty --keyserver pool.sks-keyservers.net --recv-keys "$key"; \
+  done
+
+ARG NODE_MAJOR=11
+ENV NODE_MAJOR ${NODE_MAJOR}
+
+RUN NODE_VERSION=$(curl -SL "https://nodejs.org/dist/index.tab" \
+  | grep "^v$NODE_MAJOR" \
+  | head -n 1 | awk '{ print substr($1,2) }') \
+  && ARCH= && dpkgArch="$(dpkg --print-architecture)" \
+  && case "${dpkgArch##*-}" in \
+    amd64) ARCH='x64';; \
+    ppc64el) ARCH='ppc64le';; \
+    s390x) ARCH='s390x';; \
+    arm64) ARCH='arm64';; \
+    armhf) ARCH='armv7l';; \
+    i386) ARCH='x86';; \
+    *) echo "unsupported architecture"; exit 1 ;; \
+  esac \
+  && curl -SLO "https://nodejs.org/dist/v$NODE_VERSION/node-v$NODE_VERSION-linux-$ARCH.tar.xz" \
+  && curl -SLO --compressed "https://nodejs.org/dist/v$NODE_VERSION/SHASUMS256.txt.asc" \
+  && gpg --batch --decrypt --output SHASUMS256.txt SHASUMS256.txt.asc \
+  && grep " node-v$NODE_VERSION-linux-$ARCH.tar.xz\$" SHASUMS256.txt | sha256sum -c - \
+  && tar -xJf "node-v$NODE_VERSION-linux-$ARCH.tar.xz" -C /usr/local --strip-components=1 --no-same-owner \
+  && rm "node-v$NODE_VERSION-linux-$ARCH.tar.xz" SHASUMS256.txt.asc SHASUMS256.txt \
+  && ln -s /usr/local/bin/node /usr/local/bin/nodejs
+
+RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | gpg --import
+RUN YARN_VERSION=$(curl -sSL --compressed https://yarnpkg.com/latest-version) \
+  set -ex \
+  && curl -fSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz" \
+  && curl -fSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz.asc" \
+  && gpg --batch --verify yarn-v$YARN_VERSION.tar.gz.asc yarn-v$YARN_VERSION.tar.gz \
+  && mkdir -p /opt \
+  && tar -xzf yarn-v$YARN_VERSION.tar.gz -C /opt/ \
+  && ln -s /opt/yarn-v$YARN_VERSION/bin/yarn /usr/local/bin/yarn \
+  && ln -s /opt/yarn-v$YARN_VERSION/bin/yarnpkg /usr/local/bin/yarnpkg \
+  && rm yarn-v$YARN_VERSION.tar.gz.asc yarn-v$YARN_VERSION.tar.gz
+
+CMD ruby -v && echo -n "node " && node -v && echo -n "yarn " && yarn -v && ls -la /usr/local/bin