diff --git a/.travis.yml b/.travis.yml
index 36d14e95c6..1b6b43b65f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,20 +2,28 @@ language: bash
 services: docker
 
 env:
+  - VERSION=2.6-rc VARIANT=buster
+  - VERSION=2.6-rc VARIANT=buster/slim
   - VERSION=2.6-rc VARIANT=stretch
   - VERSION=2.6-rc VARIANT=stretch/slim
   - VERSION=2.6-rc VARIANT=alpine3.8
   - VERSION=2.6-rc VARIANT=alpine3.7
+  - VERSION=2.5 VARIANT=buster
+  - VERSION=2.5 VARIANT=buster/slim
   - VERSION=2.5 VARIANT=stretch
   - VERSION=2.5 VARIANT=stretch/slim
   - VERSION=2.5 VARIANT=alpine3.8
   - VERSION=2.5 VARIANT=alpine3.7
+  - VERSION=2.4 VARIANT=buster
+  - VERSION=2.4 VARIANT=buster/slim
   - VERSION=2.4 VARIANT=stretch
   - VERSION=2.4 VARIANT=stretch/slim
   - VERSION=2.4 VARIANT=jessie
   - VERSION=2.4 VARIANT=jessie/slim
   - VERSION=2.4 VARIANT=alpine3.8
   - VERSION=2.4 VARIANT=alpine3.7
+  - VERSION=2.3 VARIANT=buster
+  - VERSION=2.3 VARIANT=buster/slim
   - VERSION=2.3 VARIANT=stretch
   - VERSION=2.3 VARIANT=stretch/slim
   - VERSION=2.3 VARIANT=jessie
diff --git a/2.3/buster/Dockerfile b/2.3/buster/Dockerfile
new file mode 100644
index 0000000000..7774c7e8e8
--- /dev/null
+++ b/2.3/buster/Dockerfile
@@ -0,0 +1,79 @@
+FROM buildpack-deps:buster
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.3
+ENV RUBY_VERSION 2.3.8
+ENV RUBY_DOWNLOAD_SHA256 910f635d84fd0d81ac9bdee0731279e6026cb4cd1315bbbb5dfb22e09c5c1dfe
+ENV RUBYGEMS_VERSION 2.7.8
+ENV BUNDLER_VERSION 1.17.1
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		bison \
+		dpkg-dev \
+		libgdbm-dev \
+		# ruby 2.3 on stretch can only support libssl1.0-dev (libssl dev from buildpack-deps is 1.1.x)
+		libssl1.0-dev \
+		ruby \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.3/buster/slim/Dockerfile b/2.3/buster/slim/Dockerfile
new file mode 100644
index 0000000000..418126253d
--- /dev/null
+++ b/2.3/buster/slim/Dockerfile
@@ -0,0 +1,103 @@
+FROM debian:buster
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		gdbm-l10n \
+		libssl1.0-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.3
+ENV RUBY_VERSION 2.3.8
+ENV RUBY_DOWNLOAD_SHA256 910f635d84fd0d81ac9bdee0731279e6026cb4cd1315bbbb5dfb22e09c5c1dfe
+ENV RUBYGEMS_VERSION 2.7.8
+ENV BUNDLER_VERSION 1.17.1
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		autoconf \
+		bison \
+		dpkg-dev \
+		gcc \
+		libbz2-dev \
+		libgdbm-dev \
+		libglib2.0-dev \
+		libncurses-dev \
+		libreadline-dev \
+		libxml2-dev \
+		libxslt-dev \
+		make \
+		ruby \
+		wget \
+		xz-utils \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& dpkg-query --show --showformat '${package}\n' \
+		| grep -P '^libreadline\d+$' \
+		| xargs apt-mark manual \
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.4/buster/Dockerfile b/2.4/buster/Dockerfile
new file mode 100644
index 0000000000..1b6c83f5c8
--- /dev/null
+++ b/2.4/buster/Dockerfile
@@ -0,0 +1,77 @@
+FROM buildpack-deps:buster
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.4
+ENV RUBY_VERSION 2.4.5
+ENV RUBY_DOWNLOAD_SHA256 2f0cdcce9989f63ef7c2939bdb17b1ef244c4f384d85b8531d60e73d8cc31eeb
+ENV RUBYGEMS_VERSION 2.7.8
+ENV BUNDLER_VERSION 1.17.1
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		bison \
+		dpkg-dev \
+		libgdbm-dev \
+		ruby \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.4/buster/slim/Dockerfile b/2.4/buster/slim/Dockerfile
new file mode 100644
index 0000000000..34acdf441e
--- /dev/null
+++ b/2.4/buster/slim/Dockerfile
@@ -0,0 +1,103 @@
+FROM debian:buster
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		gdbm-l10n \
+		libssl-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.4
+ENV RUBY_VERSION 2.4.5
+ENV RUBY_DOWNLOAD_SHA256 2f0cdcce9989f63ef7c2939bdb17b1ef244c4f384d85b8531d60e73d8cc31eeb
+ENV RUBYGEMS_VERSION 2.7.8
+ENV BUNDLER_VERSION 1.17.1
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		autoconf \
+		bison \
+		dpkg-dev \
+		gcc \
+		libbz2-dev \
+		libgdbm-dev \
+		libglib2.0-dev \
+		libncurses-dev \
+		libreadline-dev \
+		libxml2-dev \
+		libxslt-dev \
+		make \
+		ruby \
+		wget \
+		xz-utils \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& dpkg-query --show --showformat '${package}\n' \
+		| grep -P '^libreadline\d+$' \
+		| xargs apt-mark manual \
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.5/buster/Dockerfile b/2.5/buster/Dockerfile
new file mode 100644
index 0000000000..2e34af915b
--- /dev/null
+++ b/2.5/buster/Dockerfile
@@ -0,0 +1,77 @@
+FROM buildpack-deps:buster
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.5
+ENV RUBY_VERSION 2.5.3
+ENV RUBY_DOWNLOAD_SHA256 1cc9d0359a8ea35fc6111ec830d12e60168f3b9b305a3c2578357d360fcf306f
+ENV RUBYGEMS_VERSION 2.7.8
+ENV BUNDLER_VERSION 1.17.1
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		bison \
+		dpkg-dev \
+		libgdbm-dev \
+		ruby \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.5/buster/slim/Dockerfile b/2.5/buster/slim/Dockerfile
new file mode 100644
index 0000000000..a71c2b1eb9
--- /dev/null
+++ b/2.5/buster/slim/Dockerfile
@@ -0,0 +1,103 @@
+FROM debian:buster
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		gdbm-l10n \
+		libssl-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.5
+ENV RUBY_VERSION 2.5.3
+ENV RUBY_DOWNLOAD_SHA256 1cc9d0359a8ea35fc6111ec830d12e60168f3b9b305a3c2578357d360fcf306f
+ENV RUBYGEMS_VERSION 2.7.8
+ENV BUNDLER_VERSION 1.17.1
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		autoconf \
+		bison \
+		dpkg-dev \
+		gcc \
+		libbz2-dev \
+		libgdbm-dev \
+		libglib2.0-dev \
+		libncurses-dev \
+		libreadline-dev \
+		libxml2-dev \
+		libxslt-dev \
+		make \
+		ruby \
+		wget \
+		xz-utils \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& dpkg-query --show --showformat '${package}\n' \
+		| grep -P '^libreadline\d+$' \
+		| xargs apt-mark manual \
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.6-rc/buster/Dockerfile b/2.6-rc/buster/Dockerfile
new file mode 100644
index 0000000000..6da962e260
--- /dev/null
+++ b/2.6-rc/buster/Dockerfile
@@ -0,0 +1,77 @@
+FROM buildpack-deps:buster
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.6-rc
+ENV RUBY_VERSION 2.6.0-preview3
+ENV RUBY_DOWNLOAD_SHA256 9856d9e0e32df9e5cdf01928eec363d037f1a76dab2abbf828170647beaf64fe
+ENV RUBYGEMS_VERSION 2.7.8
+ENV BUNDLER_VERSION 1.17.1
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		bison \
+		dpkg-dev \
+		libgdbm-dev \
+		ruby \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.6-rc/buster/slim/Dockerfile b/2.6-rc/buster/slim/Dockerfile
new file mode 100644
index 0000000000..5bb7a944b3
--- /dev/null
+++ b/2.6-rc/buster/slim/Dockerfile
@@ -0,0 +1,103 @@
+FROM debian:buster
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		gdbm-l10n \
+		libssl-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.6-rc
+ENV RUBY_VERSION 2.6.0-preview3
+ENV RUBY_DOWNLOAD_SHA256 9856d9e0e32df9e5cdf01928eec363d037f1a76dab2abbf828170647beaf64fe
+ENV RUBYGEMS_VERSION 2.7.8
+ENV BUNDLER_VERSION 1.17.1
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		autoconf \
+		bison \
+		dpkg-dev \
+		gcc \
+		libbz2-dev \
+		libgdbm-dev \
+		libglib2.0-dev \
+		libncurses-dev \
+		libreadline-dev \
+		libxml2-dev \
+		libxslt-dev \
+		make \
+		ruby \
+		wget \
+		xz-utils \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& dpkg-query --show --showformat '${package}\n' \
+		| grep -P '^libreadline\d+$' \
+		| xargs apt-mark manual \
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/update.sh b/update.sh
old mode 100755
new mode 100644
index 0c1222932e..4c002fa103
--- a/update.sh
+++ b/update.sh
@@ -67,7 +67,7 @@ for version in "${versions[@]}"; do
 
 	for v in \
 		alpine{3.6,3.7,3.8} \
-		{jessie,stretch}{/slim,} \
+		{jessie,stretch,buster}{/slim,} \
 	; do
 		dir="$version/$v"
 		variant="$(basename "$v")"
@@ -90,10 +90,17 @@ for version in "${versions[@]}"; do
 			-e "$(
 				if [ "$version" = 2.3 ] && [[ "$v" = stretch* ]]; then
 					echo 's/libssl-dev/libssl1.0-dev/g'
+				elif [ "$version" = 2.3 ] && [[ "$v" = buster* ]]; then
+					echo 's/libssl-dev/libssl1.0-dev/g'
 				else
 					echo '/libssl1.0-dev/d'
 				fi
 			)" \
+			-e "$(
+				if [[ "$v" = buster* ]]; then
+					echo 's/libgdbm3/gdbm-l10n/g'
+				fi
+			)" \
 			-e 's/^(FROM (debian|buildpack-deps|alpine)):.*/\1:'"$tag"'/' \
 			"$template" > "$dir/Dockerfile"