Ruan Bekker's Blog

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Running Java Web Applications on Tomcat With Docker Swarm

From this post we used Payara Micro to Setup a Web Application, and a full example was provided on how to create a war file that will be used for the deployment.

Today we will be using Tomcat to deploy the same application. The official repository can be found on hub.docker.com/_/tomcat .

Our Dockerfile for our Own Tomcat Image:

The Dockerfile is modified a bit (CATALINA_OPTS) to be able to pass JVM environment variables, but if you would like to use the standard image you can skip this and just use the image from their repository.

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FROM openjdk:8-jre-alpine

ENV CATALINA_HOME /usr/local/tomcat
ENV PATH $CATALINA_HOME/bin:$PATH
RUN mkdir -p "$CATALINA_HOME"
WORKDIR $CATALINA_HOME
ENV CATALINA_OPTS -Xmx768m -Xms512m -XX:PermSize=256m -XX:MaxPermSize=512m -XX:ReservedCodeCacheSize=64m -XX:+UseG1GC -XX:+CMSClassUnloadingEnabled -XX:+PrintHeapAtGC -XX:+PrintGCDetails -XX:+PrintGCTimeStamps
# let "Tomcat Native" live somewhere isolated
ENV TOMCAT_NATIVE_LIBDIR $CATALINA_HOME/native-jni-lib
ENV LD_LIBRARY_PATH ${LD_LIBRARY_PATH:+$LD_LIBRARY_PATH:}$TOMCAT_NATIVE_LIBDIR

RUN apk add --no-cache gnupg

# see https://www.apache.org/dist/tomcat/tomcat-$TOMCAT_MAJOR/KEYS
# see also "update.sh" (https://github.com/docker-library/tomcat/blob/master/update.sh)
ENV GPG_KEYS 05AB33110949707C93A279E3D3EFE6B686867BA6 07E48665A34DCAFAE522E5E6266191C37C037D42 47309207D818FFD8DCD3F83F1931D684307A10A5 541FBE7D8F78B25E055DDEE13C370389288584E7 61B832AC2F1C5A90F0F9B00A1C506407564C17A3 713DA88BE50911535FE716F5208B0AB1D63011C7 79F7026C690BAA50B92CD8B66A3AD3F4F22C4FED 9BA44C2621385CB966EBA586F72C284D731FABEE A27677289986DB50844682F8ACB77FC2E86E29AC A9C5DF4D22E99998D9875A5110C01C5A2F6059E7 DCFD35E0BF8CA7344752DE8B6FB21E8933C60243 F3A04C595DB5B6A5F1ECA43E3B7BBB100D811BBE F7DA48BB64BCB84ECBA7EE6935CD23C10D498E23
RUN set -ex; \
  for key in $GPG_KEYS; do \
      gpg --keyserver ha.pool.sks-keyservers.net --recv-keys "$key"; \
  done

ENV TOMCAT_MAJOR 8
ENV TOMCAT_VERSION 8.5.23
ENV TOMCAT_SHA1 1ba27c1bb86ab9c8404e98068800f90bd662523c

ENV TOMCAT_TGZ_URLS \
# https://issues.apache.org/jira/browse/INFRA-8753?focusedCommentId=14735394#comment-14735394
  https://www.apache.org/dyn/closer.cgi?action=download&filename=tomcat/tomcat-$TOMCAT_MAJOR/v$TOMCAT_VERSION/bin/apache-tomcat-$TOMCAT_VERSION.tar.gz \
# if the version is outdated, we might have to pull from the dist/archive :/
  https://www-us.apache.org/dist/tomcat/tomcat-$TOMCAT_MAJOR/v$TOMCAT_VERSION/bin/apache-tomcat-$TOMCAT_VERSION.tar.gz \
  https://www.apache.org/dist/tomcat/tomcat-$TOMCAT_MAJOR/v$TOMCAT_VERSION/bin/apache-tomcat-$TOMCAT_VERSION.tar.gz \
  https://archive.apache.org/dist/tomcat/tomcat-$TOMCAT_MAJOR/v$TOMCAT_VERSION/bin/apache-tomcat-$TOMCAT_VERSION.tar.gz

ENV TOMCAT_ASC_URLS \
  https://www.apache.org/dyn/closer.cgi?action=download&filename=tomcat/tomcat-$TOMCAT_MAJOR/v$TOMCAT_VERSION/bin/apache-tomcat-$TOMCAT_VERSION.tar.gz.asc \
# not all the mirrors actually carry the .asc files :'(
  https://www-us.apache.org/dist/tomcat/tomcat-$TOMCAT_MAJOR/v$TOMCAT_VERSION/bin/apache-tomcat-$TOMCAT_VERSION.tar.gz.asc \
  https://www.apache.org/dist/tomcat/tomcat-$TOMCAT_MAJOR/v$TOMCAT_VERSION/bin/apache-tomcat-$TOMCAT_VERSION.tar.gz.asc \
  https://archive.apache.org/dist/tomcat/tomcat-$TOMCAT_MAJOR/v$TOMCAT_VERSION/bin/apache-tomcat-$TOMCAT_VERSION.tar.gz.asc

RUN set -eux; \
  \
  apk add --no-cache --virtual .fetch-deps \
      ca-certificates \
      openssl \
  ; \
  \
  success=; \
  for url in $TOMCAT_TGZ_URLS; do \
      if wget -O tomcat.tar.gz "$url"; then \
          success=1; \
          break; \
      fi; \
  done; \
  [ -n "$success" ]; \
  \
  echo "$TOMCAT_SHA1 *tomcat.tar.gz" | sha1sum -c -; \
  \
  success=; \
  for url in $TOMCAT_ASC_URLS; do \
      if wget -O tomcat.tar.gz.asc "$url"; then \
          success=1; \
          break; \
      fi; \
  done; \
  [ -n "$success" ]; \
  \
  gpg --batch --verify tomcat.tar.gz.asc tomcat.tar.gz; \
  tar -xvf tomcat.tar.gz --strip-components=1; \
  rm bin/*.bat; \
  rm tomcat.tar.gz*; \
  \
  nativeBuildDir="$(mktemp -d)"; \
  tar -xvf bin/tomcat-native.tar.gz -C "$nativeBuildDir" --strip-components=1; \
  apk add --no-cache --virtual .native-build-deps \
      apr-dev \
      coreutils \
      dpkg-dev dpkg \
      gcc \
      libc-dev \
      make \
      "openjdk${JAVA_VERSION%%[-~bu]*}"="$JAVA_ALPINE_VERSION" \
      openssl-dev \
  ; \
  ( \
      export CATALINA_HOME="$PWD"; \
      cd "$nativeBuildDir/native"; \
      gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)"; \
      ./configure \
          --build="$gnuArch" \
          --libdir="$TOMCAT_NATIVE_LIBDIR" \
          --prefix="$CATALINA_HOME" \
          --with-apr="$(which apr-1-config)" \
          --with-java-home="$(docker-java-home)" \
          --with-ssl=yes; \
      make -j "$(nproc)"; \
      make install; \
  ); \
  runDeps="$( \
     scanelf --needed --nobanner --format '%n#p' --recursive "$TOMCAT_NATIVE_LIBDIR" \
         | tr ',' '\n' \
         | sort -u \
         | awk 'system("[ -e /usr/local/lib/" $1 " ]") == 0 { next } { print "so:" $1 }' \
 )"; \
  apk add --virtual .tomcat-native-rundeps $runDeps; \
  apk del .fetch-deps .native-build-deps; \
  rm -rf "$nativeBuildDir"; \
  rm bin/tomcat-native.tar.gz; \
  \
# sh removes env vars it doesn't support (ones with periods)
# https://github.com/docker-library/tomcat/issues/77
  apk add --no-cache bash; \
  find ./bin/ -name '*.sh' -exec sed -ri 's|^#!/bin/sh$|#!/usr/bin/env bash|' '{}' +

# verify Tomcat Native is working properly
RUN set -e \
  && nativeLines="$(catalina.sh configtest 2>&1)" \
  && nativeLines="$(echo "$nativeLines" | grep 'Apache Tomcat Native')" \
  && nativeLines="$(echo "$nativeLines" | sort -u)" \
  && if ! echo "$nativeLines" | grep 'INFO: Loaded APR based Apache Tomcat Native library' >&2; then \
      echo >&2 "$nativeLines"; \
      exit 1; \
  fi

EXPOSE 8080
CMD ["catalina.sh", "run"]

Building our Image and Pusing to our Registry:

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$ docker build -t registry.gitlab.com/<user>/<repo>/<image>:<tag>
$ docker push registry.gitlab.com/<user>/<repo>/<image>:<tag>

Dockerfile for our Application:

Now that we have built our image for Tomcat, we can write our Dockerfile for our application, note that the hello.war file also needs to be in the same working directory, unless written otherwise:

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FROM registry.gitlab.com/<user>/<repo>/<image>:<tag>
COPY hello.war /usr/local/tomcat/webapps/hello.war

Setup the Compose file for our Stack:

We will use docker stack to deploy our application, note that I have Traefik that acts as my reverse proxy.

Below, our app.yml compose file:

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version: '3'

services:
  hello:
    image: registry.gitlab.com/<user>/<repo>/<image>:<tag>
    networks:
      - appnet
    deploy:
      labels:
        - "traefik.port=8080"
        - "traefik.docker.network=appnet"
        - "traefik.frontend.rule=Host:apps.mydomain.com; PathPrefix: /hello/"
      mode: replicated
      replicas: 1
      placement:
        constraints:
          - 'node.role==worker'

networks:
  appnet:
    external: true

Deploy our Application:

From our compose file we defined that our network is external, so if you are using the same name, and you have not yet setup the overlay network:

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$ docker network create --driver overlay appnet

Now deploy the stack:

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$ docker stack deploy --compose-file app.yml apps

Testing our Application:

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$ curl http://apps.mydomain.com/hello/

<!DOCTYPE html>
<html>
            Hello World!
   Test Page with Docker + Payara Micro</h3>

   Serving From ContainerId: d24f8cd982fc
</html>