diff --git a/.swiftformat b/.swiftformat
index 1084e4c..e639ee7 100644
--- a/.swiftformat
+++ b/.swiftformat
@@ -1,10 +1,12 @@
 # file options
 
+--exclude .build
+
 # format options
 
---self insert 
---patternlet inline 
---stripunusedargs unnamed-only 
+--self insert
+--patternlet inline
+--stripunusedargs unnamed-only
 --comments ignore
 
 # rules
diff --git a/Sources/CoreMetrics/Metrics.swift b/Sources/CoreMetrics/Metrics.swift
index dd5d0ef..4328087 100644
--- a/Sources/CoreMetrics/Metrics.swift
+++ b/Sources/CoreMetrics/Metrics.swift
@@ -84,7 +84,6 @@ public class Counter {
     }
 }
 
-
 public extension Recorder {
     /// Create a new `Recorder`.
     ///
@@ -153,7 +152,6 @@ public class Recorder {
     }
 }
 
-
 /// A gauge is a metric that represents a single numerical value that can arbitrarily go up and down.
 /// Gauges are typically used for measured values like temperatures or current memory usage, but also "counts" that can go up and down, like the number of active threads.
 /// Gauges are modeled as `Recorder` with a sample size of 1 and that does not perform any aggregation.
@@ -168,7 +166,6 @@ public class Gauge: Recorder {
     }
 }
 
-
 public extension Timer {
     /// Create a new `Timer`.
     ///
@@ -572,9 +569,11 @@ public final class NOOPMetricsHandler: MetricsFactory, CounterHandler, RecorderH
     public func makeCounter(label: String, dimensions: [(String, String)]) -> CounterHandler {
         return self
     }
+
     public func makeRecorder(label: String, dimensions: [(String, String)], aggregate: Bool) -> RecorderHandler {
         return self
     }
+
     public func makeTimer(label: String, dimensions: [(String, String)]) -> TimerHandler {
         return self
     }
diff --git a/docker/Dockerfile b/docker/Dockerfile
index 5be33fc..cbb86f7 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -1,56 +1,37 @@
-ARG ubuntu_version=18.04
-FROM ubuntu:$ubuntu_version
+ARG swift_version=5.0
+ARG ubuntu_version=bionic
+# backwards compatibility for 4.2 images
+ARG image_version=$swift_version-$ubuntu_version
+FROM swift:$image_version
 # needed to do again after FROM due to docker limitation
+ARG swift_version
 ARG ubuntu_version
 
-ARG DEBIAN_FRONTEND=noninteractive
-# do not start services during installation as this will fail and log a warning / error.
-RUN echo "#!/bin/sh\nexit 0" > /usr/sbin/policy-rc.d
+# set as UTF-8
+RUN apt-get update && apt-get install -y locales locales-all
+ENV LC_ALL en_US.UTF-8
+ENV LANG en_US.UTF-8
+ENV LANGUAGE en_US.UTF-8
 
-# basic dependencies
-RUN apt-get update && apt-get install -y wget git build-essential software-properties-common pkg-config locales
-RUN apt-get update && apt-get install -y libicu-dev libblocksruntime0 curl libcurl4-openssl-dev libz-dev
-
-# local
-RUN locale-gen en_US.UTF-8
-RUN locale-gen en_US en_US.UTF-8
-RUN dpkg-reconfigure locales
-RUN echo 'export LANG=en_US.UTF-8' >> $HOME/.profile
-RUN echo 'export LANGUAGE=en_US:en' >> $HOME/.profile
-RUN echo 'export LC_ALL=en_US.UTF-8' >> $HOME/.profile
-
-# known_hosts
-RUN mkdir -p $HOME/.ssh
-RUN touch $HOME/.ssh/known_hosts
-RUN ssh-keyscan github.com 2> /dev/null >> $HOME/.ssh/known_hosts
-
-# clang
-RUN apt-get update && apt-get install -y clang-3.9
-RUN update-alternatives --install /usr/bin/clang clang /usr/bin/clang-3.9 100
-RUN update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-3.9 100
+# dependencies
+RUN apt-get update && apt-get install -y wget
+RUN apt-get update && apt-get install -y lsof dnsutils netcat-openbsd net-tools # used by integration tests
 
 # ruby and jazzy for docs generation
-#ARG skip_ruby_from_ppa
-#RUN [ -n "$skip_ruby_from_ppa" ] || apt-add-repository -y ppa:brightbox/ruby-ng
-#RUN [ -n "$skip_ruby_from_ppa" ] || { apt-get update && apt-get install -y ruby2.4 ruby2.4-dev; }
-#RUN [ -z "$skip_ruby_from_ppa" ] || { apt-get update && apt-get install -y ruby ruby-dev; }
-#RUN apt-get update && apt-get install -y libsqlite3-dev
 RUN apt-get update && apt-get install -y ruby ruby-dev libsqlite3-dev
 RUN gem install jazzy --no-ri --no-rdoc
 
-# swift
-ARG swift_version=4.2.3
-ARG swift_flavour=RELEASE
-ARG swift_builds_suffix=release
+# tools
+RUN mkdir -p $HOME/.tools
+RUN echo 'export PATH="$HOME/.tools:$PATH"' >> $HOME/.profile
 
-RUN mkdir $HOME/.swift
-RUN wget -q "https://swift.org/builds/swift-${swift_version}-${swift_builds_suffix}/ubuntu$(echo $ubuntu_version | sed 's/\.//g')/swift-${swift_version}-${swift_flavour}/swift-${swift_version}-${swift_flavour}-ubuntu${ubuntu_version}.tar.gz" -O $HOME/swift.tar.gz
-RUN tar xzf $HOME/swift.tar.gz --directory $HOME/.swift --strip-components=1
-RUN echo 'export PATH="$HOME/.swift/usr/bin:$PATH"' >> $HOME/.profile
-RUN echo 'export LINUX_SOURCEKIT_LIB_PATH="$HOME/.swift/usr/lib"' >> $HOME/.profile
+# script to allow mapping framepointers on linux (until part of the toolchain)
+RUN wget -q https://raw.githubusercontent.com/apple/swift/master/utils/symbolicate-linux-fatal -O $HOME/.tools/symbolicate-linux-fatal
+RUN chmod 755 $HOME/.tools/symbolicate-linux-fatal
 
-# script to allow mapping framepointers on linux
-RUN mkdir -p $HOME/.scripts
-RUN wget -q https://raw.githubusercontent.com/apple/swift/master/utils/symbolicate-linux-fatal -O $HOME/.scripts/symbolicate-linux-fatal
-RUN chmod 755 $HOME/.scripts/symbolicate-linux-fatal
-RUN echo 'export PATH="$HOME/.scripts:$PATH"' >> $HOME/.profile
+# swiftformat (until part of the toolchain)
+
+ARG swiftformat_version=0.40.11
+RUN git clone --branch $swiftformat_version --depth 1 https://github.com/nicklockwood/SwiftFormat $HOME/.tools/swift-format
+RUN cd $HOME/.tools/swift-format && swift build -c release
+RUN ln -s $HOME/.tools/swift-format/.build/release/swiftformat $HOME/.tools/swiftformat
diff --git a/docker/docker-compose.1804.42.yaml b/docker/docker-compose.1804.42.yaml
index 6c8a962..a989e28 100644
--- a/docker/docker-compose.1804.42.yaml
+++ b/docker/docker-compose.1804.42.yaml
@@ -6,8 +6,7 @@ services:
     image: swift-metrics:18.04-4.2
     build:
       args:
-        ubuntu_version: "18.04"
-        swift_version: "4.2"
+        image_version: "4.2"
 
   test:
     image: swift-metrics:18.04-4.2
diff --git a/docker/docker-compose.1804.50.yaml b/docker/docker-compose.1804.50.yaml
index 2c1317a..9c760cf 100644
--- a/docker/docker-compose.1804.50.yaml
+++ b/docker/docker-compose.1804.50.yaml
@@ -6,7 +6,7 @@ services:
     image: swift-metrics:18.04-5.0
     build:
       args:
-        ubuntu_version: "18.04"
+        ubuntu_version: "bionic"
         swift_version: "5.0"
 
   test:
diff --git a/scripts/sanity.sh b/scripts/sanity.sh
index 34d9350..6e73704 100755
--- a/scripts/sanity.sh
+++ b/scripts/sanity.sh
@@ -47,10 +47,23 @@ else
   printf "\033[0;32mokay.\033[0m\n"
 fi
 
-printf "=> Checking license headers... "
+printf "=> Checking format... "
+FIRST_OUT="$(git status --porcelain)"
+swiftformat . > /dev/null 2>&1
+SECOND_OUT="$(git status --porcelain)"
+if [[ "$FIRST_OUT" != "$SECOND_OUT" ]]; then
+  printf "\033[0;31mformatting issues!\033[0m\n"
+  git --no-pager diff
+  exit 1
+else
+  printf "\033[0;32mokay.\033[0m\n"
+fi
+
+printf "=> Checking license headers\n"
 tmp=$(mktemp /tmp/.swift-metrics-sanity_XXXXXX)
 
 for language in swift-or-c bash dtrace; do
+  printf "   * $language... "
   declare -a matching_files
   declare -a exceptions
   expections=( )