#2681 : add messaging design pattern implementation with kafka #2712
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| ## MESSAGING DESIGN PATTERN | ||
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| ### Also Known As : | ||
| Event Driven / Message Stream Based MicroService | ||
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| ### Intent: | ||
| Sample implementation for Kafka Bases messaging service | ||
| and events will be published based on transactions | ||
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| ### Explanation | ||
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| Use asynchronous messaging for inter-service communication. Services communicating by exchanging messages over messaging channels. | ||
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| There are several different styles of asynchronous communication: | ||
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| Request/response - a service sends a request message to a recipient and expects to receive a reply message promptly | ||
| Notifications - a sender sends a message a recipient but does not expect a reply. Nor is one sent. | ||
| Request/asynchronous response - a service sends a request message to a recipient and expects to receive a reply message eventually | ||
| Publish/subscribe - a service publishes a message to zero or more recipients | ||
| Publish/asynchronous response - a service publishes a request to one or recipients, some of whom send back a reply | ||
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| #### This pattern has the following benefits: | ||
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| Loose runtime coupling since it decouples the message sender from the consumer | ||
| * Improved availability since the message broker buffers messages until the consumer is able to process them | ||
| * Supports a variety of communication patterns including request/reply, notifications, request/async response, publish/subscribe, publish/async response etc | ||
| * This pattern has the following drawbacks: | ||
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| ### Class diagram: | ||
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| #### High Level Design: | ||
|  | ||
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| ### Applicability: | ||
| * Its more appropriate where the system expecting Pub/Sub based communication | ||
| * If immediate notification is required between two microservices, then this pattern will help on the same | ||
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| ### Tutorials : | ||
| 1. https://medium.com/design-microservices-architecture-with-patterns/microservices-asynchronous-message-based-communication-6643bee06123 | ||
| 2. https://microservices.io/patterns/communication-style/messaging.html | ||
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| ### Known uses: | ||
| * Event Driven MicroService - Communication between more than one microservice using messaging channel | ||
| * Distributed Transaction Service - Auditing and Notifying system from one to another | ||
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| ### Consequences: | ||
| Additional complexity of message broker, which must be highly available | ||
| This pattern has the following issues: | ||
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| - Request/reply-style communication is more complex | ||
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| ### Related patterns : | ||
| * The Saga pattern and CQRS pattern use messaging : https://microservices.io/patterns/data/saga.html , https://microservices.io/patterns/data/cqrs.html | ||
| * The Transactional Outbox pattern enables messages to be sent as part of a database transaction : https://microservices.io/patterns/data/transactional-outbox.html | ||
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| ### Credits: | ||
| ``` Chris Richardson ``` | ||
| Experienced software architect, author of POJOs in Action, the creator of the original CloudFoundry.com | ||
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| #!/bin/sh | ||
| # ---------------------------------------------------------------------------- | ||
| # Licensed to the Apache Software Foundation (ASF) under one | ||
| # or more contributor license agreements. See the NOTICE file | ||
| # distributed with this work for additional information | ||
| # regarding copyright ownership. The ASF licenses this file | ||
| # to you under the Apache License, Version 2.0 (the | ||
| # "License"); you may not use this file except in compliance | ||
| # with the License. You may obtain a copy of the License at | ||
| # | ||
| # https://www.apache.org/licenses/LICENSE-2.0 | ||
| # | ||
| # Unless required by applicable law or agreed to in writing, | ||
| # software distributed under the License is distributed on an | ||
| # "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | ||
| # KIND, either express or implied. See the License for the | ||
| # specific language governing permissions and limitations | ||
| # under the License. | ||
| # ---------------------------------------------------------------------------- | ||
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| # ---------------------------------------------------------------------------- | ||
| # Apache Maven Wrapper startup batch script, version 3.2.0 | ||
| # | ||
| # Required ENV vars: | ||
| # ------------------ | ||
| # JAVA_HOME - location of a JDK home dir | ||
| # | ||
| # Optional ENV vars | ||
| # ----------------- | ||
| # MAVEN_OPTS - parameters passed to the Java VM when running Maven | ||
| # e.g. to debug Maven itself, use | ||
| # set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000 | ||
| # MAVEN_SKIP_RC - flag to disable loading of mavenrc files | ||
| # ---------------------------------------------------------------------------- | ||
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| if [ -z "$MAVEN_SKIP_RC" ] ; then | ||
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| if [ -f /usr/local/etc/mavenrc ] ; then | ||
| . /usr/local/etc/mavenrc | ||
| fi | ||
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| if [ -f /etc/mavenrc ] ; then | ||
| . /etc/mavenrc | ||
| fi | ||
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| if [ -f "$HOME/.mavenrc" ] ; then | ||
| . "$HOME/.mavenrc" | ||
| fi | ||
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| fi | ||
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| # OS specific support. $var _must_ be set to either true or false. | ||
| cygwin=false; | ||
| darwin=false; | ||
| mingw=false | ||
| case "$(uname)" in | ||
| CYGWIN*) cygwin=true ;; | ||
| MINGW*) mingw=true;; | ||
| Darwin*) darwin=true | ||
| # Use /usr/libexec/java_home if available, otherwise fall back to /Library/Java/Home | ||
| # See https://developer.apple.com/library/mac/qa/qa1170/_index.html | ||
| if [ -z "$JAVA_HOME" ]; then | ||
| if [ -x "/usr/libexec/java_home" ]; then | ||
| JAVA_HOME="$(/usr/libexec/java_home)"; export JAVA_HOME | ||
| else | ||
| JAVA_HOME="/Library/Java/Home"; export JAVA_HOME | ||
| fi | ||
| fi | ||
| ;; | ||
| esac | ||
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| if [ -z "$JAVA_HOME" ] ; then | ||
| if [ -r /etc/gentoo-release ] ; then | ||
| JAVA_HOME=$(java-config --jre-home) | ||
| fi | ||
| fi | ||
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| # For Cygwin, ensure paths are in UNIX format before anything is touched | ||
| if $cygwin ; then | ||
| [ -n "$JAVA_HOME" ] && | ||
| JAVA_HOME=$(cygpath --unix "$JAVA_HOME") | ||
| [ -n "$CLASSPATH" ] && | ||
| CLASSPATH=$(cygpath --path --unix "$CLASSPATH") | ||
| fi | ||
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| # For Mingw, ensure paths are in UNIX format before anything is touched | ||
| if $mingw ; then | ||
| [ -n "$JAVA_HOME" ] && [ -d "$JAVA_HOME" ] && | ||
| JAVA_HOME="$(cd "$JAVA_HOME" || (echo "cannot cd into $JAVA_HOME."; exit 1); pwd)" | ||
| fi | ||
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| if [ -z "$JAVA_HOME" ]; then | ||
| javaExecutable="$(which javac)" | ||
| if [ -n "$javaExecutable" ] && ! [ "$(expr "\"$javaExecutable\"" : '\([^ ]*\)')" = "no" ]; then | ||
| # readlink(1) is not available as standard on Solaris 10. | ||
| readLink=$(which readlink) | ||
| if [ ! "$(expr "$readLink" : '\([^ ]*\)')" = "no" ]; then | ||
| if $darwin ; then | ||
| javaHome="$(dirname "\"$javaExecutable\"")" | ||
| javaExecutable="$(cd "\"$javaHome\"" && pwd -P)/javac" | ||
| else | ||
| javaExecutable="$(readlink -f "\"$javaExecutable\"")" | ||
| fi | ||
| javaHome="$(dirname "\"$javaExecutable\"")" | ||
| javaHome=$(expr "$javaHome" : '\(.*\)/bin') | ||
| JAVA_HOME="$javaHome" | ||
| export JAVA_HOME | ||
| fi | ||
| fi | ||
| fi | ||
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| if [ -z "$JAVACMD" ] ; then | ||
| if [ -n "$JAVA_HOME" ] ; then | ||
| if [ -x "$JAVA_HOME/jre/sh/java" ] ; then | ||
| # IBM's JDK on AIX uses strange locations for the executables | ||
| JAVACMD="$JAVA_HOME/jre/sh/java" | ||
| else | ||
| JAVACMD="$JAVA_HOME/bin/java" | ||
| fi | ||
| else | ||
| JAVACMD="$(\unset -f command 2>/dev/null; \command -v java)" | ||
| fi | ||
| fi | ||
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| if [ ! -x "$JAVACMD" ] ; then | ||
| echo "Error: JAVA_HOME is not defined correctly." >&2 | ||
| echo " We cannot execute $JAVACMD" >&2 | ||
| exit 1 | ||
| fi | ||
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| if [ -z "$JAVA_HOME" ] ; then | ||
| echo "Warning: JAVA_HOME environment variable is not set." | ||
| fi | ||
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| # traverses directory structure from process work directory to filesystem root | ||
| # first directory with .mvn subdirectory is considered project base directory | ||
| find_maven_basedir() { | ||
| if [ -z "$1" ] | ||
| then | ||
| echo "Path not specified to find_maven_basedir" | ||
| return 1 | ||
| fi | ||
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| basedir="$1" | ||
| wdir="$1" | ||
| while [ "$wdir" != '/' ] ; do | ||
| if [ -d "$wdir"/.mvn ] ; then | ||
| basedir=$wdir | ||
| break | ||
| fi | ||
| # workaround for JBEAP-8937 (on Solaris 10/Sparc) | ||
| if [ -d "${wdir}" ]; then | ||
| wdir=$(cd "$wdir/.." || exit 1; pwd) | ||
| fi | ||
| # end of workaround | ||
| done | ||
| printf '%s' "$(cd "$basedir" || exit 1; pwd)" | ||
| } | ||
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| # concatenates all lines of a file | ||
| concat_lines() { | ||
| if [ -f "$1" ]; then | ||
| # Remove \r in case we run on Windows within Git Bash | ||
| # and check out the repository with auto CRLF management | ||
| # enabled. Otherwise, we may read lines that are delimited with | ||
| # \r\n and produce $'-Xarg\r' rather than -Xarg due to word | ||
| # splitting rules. | ||
| tr -s '\r\n' ' ' < "$1" | ||
| fi | ||
| } | ||
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| log() { | ||
| if [ "$MVNW_VERBOSE" = true ]; then | ||
| printf '%s\n' "$1" | ||
| fi | ||
| } | ||
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| BASE_DIR=$(find_maven_basedir "$(dirname "$0")") | ||
| if [ -z "$BASE_DIR" ]; then | ||
| exit 1; | ||
| fi | ||
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| MAVEN_PROJECTBASEDIR=${MAVEN_BASEDIR:-"$BASE_DIR"}; export MAVEN_PROJECTBASEDIR | ||
| log "$MAVEN_PROJECTBASEDIR" | ||
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| ########################################################################################## | ||
| # Extension to allow automatically downloading the maven-wrapper.jar from Maven-central | ||
| # This allows using the maven wrapper in projects that prohibit checking in binary data. | ||
| ########################################################################################## | ||
| wrapperJarPath="$MAVEN_PROJECTBASEDIR/.mvn/wrapper/maven-wrapper.jar" | ||
| if [ -r "$wrapperJarPath" ]; then | ||
| log "Found $wrapperJarPath" | ||
| else | ||
| log "Couldn't find $wrapperJarPath, downloading it ..." | ||
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| if [ -n "$MVNW_REPOURL" ]; then | ||
| wrapperUrl="$MVNW_REPOURL/org/apache/maven/wrapper/maven-wrapper/3.2.0/maven-wrapper-3.2.0.jar" | ||
| else | ||
| wrapperUrl="https://repo.maven.apache.org/maven2/org/apache/maven/wrapper/maven-wrapper/3.2.0/maven-wrapper-3.2.0.jar" | ||
| fi | ||
| while IFS="=" read -r key value; do | ||
| # Remove '\r' from value to allow usage on windows as IFS does not consider '\r' as a separator ( considers space, tab, new line ('\n'), and custom '=' ) | ||
| safeValue=$(echo "$value" | tr -d '\r') | ||
| case "$key" in (wrapperUrl) wrapperUrl="$safeValue"; break ;; | ||
| esac | ||
| done < "$MAVEN_PROJECTBASEDIR/.mvn/wrapper/maven-wrapper.properties" | ||
| log "Downloading from: $wrapperUrl" | ||
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| if $cygwin; then | ||
| wrapperJarPath=$(cygpath --path --windows "$wrapperJarPath") | ||
| fi | ||
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| if command -v wget > /dev/null; then | ||
| log "Found wget ... using wget" | ||
| [ "$MVNW_VERBOSE" = true ] && QUIET="" || QUIET="--quiet" | ||
| if [ -z "$MVNW_USERNAME" ] || [ -z "$MVNW_PASSWORD" ]; then | ||
| wget $QUIET "$wrapperUrl" -O "$wrapperJarPath" || rm -f "$wrapperJarPath" | ||
| else | ||
| wget $QUIET --http-user="$MVNW_USERNAME" --http-password="$MVNW_PASSWORD" "$wrapperUrl" -O "$wrapperJarPath" || rm -f "$wrapperJarPath" | ||
| fi | ||
| elif command -v curl > /dev/null; then | ||
| log "Found curl ... using curl" | ||
| [ "$MVNW_VERBOSE" = true ] && QUIET="" || QUIET="--silent" | ||
| if [ -z "$MVNW_USERNAME" ] || [ -z "$MVNW_PASSWORD" ]; then | ||
| curl $QUIET -o "$wrapperJarPath" "$wrapperUrl" -f -L || rm -f "$wrapperJarPath" | ||
| else | ||
| curl $QUIET --user "$MVNW_USERNAME:$MVNW_PASSWORD" -o "$wrapperJarPath" "$wrapperUrl" -f -L || rm -f "$wrapperJarPath" | ||
| fi | ||
| else | ||
| log "Falling back to using Java to download" | ||
| javaSource="$MAVEN_PROJECTBASEDIR/.mvn/wrapper/MavenWrapperDownloader.java" | ||
| javaClass="$MAVEN_PROJECTBASEDIR/.mvn/wrapper/MavenWrapperDownloader.class" | ||
| # For Cygwin, switch paths to Windows format before running javac | ||
| if $cygwin; then | ||
| javaSource=$(cygpath --path --windows "$javaSource") | ||
| javaClass=$(cygpath --path --windows "$javaClass") | ||
| fi | ||
| if [ -e "$javaSource" ]; then | ||
| if [ ! -e "$javaClass" ]; then | ||
| log " - Compiling MavenWrapperDownloader.java ..." | ||
| ("$JAVA_HOME/bin/javac" "$javaSource") | ||
| fi | ||
| if [ -e "$javaClass" ]; then | ||
| log " - Running MavenWrapperDownloader.java ..." | ||
| ("$JAVA_HOME/bin/java" -cp .mvn/wrapper MavenWrapperDownloader "$wrapperUrl" "$wrapperJarPath") || rm -f "$wrapperJarPath" | ||
| fi | ||
| fi | ||
| fi | ||
| fi | ||
| ########################################################################################## | ||
| # End of extension | ||
| ########################################################################################## | ||
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| # If specified, validate the SHA-256 sum of the Maven wrapper jar file | ||
| wrapperSha256Sum="" | ||
| while IFS="=" read -r key value; do | ||
| case "$key" in (wrapperSha256Sum) wrapperSha256Sum=$value; break ;; | ||
| esac | ||
| done < "$MAVEN_PROJECTBASEDIR/.mvn/wrapper/maven-wrapper.properties" | ||
| if [ -n "$wrapperSha256Sum" ]; then | ||
| wrapperSha256Result=false | ||
| if command -v sha256sum > /dev/null; then | ||
| if echo "$wrapperSha256Sum $wrapperJarPath" | sha256sum -c > /dev/null 2>&1; then | ||
| wrapperSha256Result=true | ||
| fi | ||
| elif command -v shasum > /dev/null; then | ||
| if echo "$wrapperSha256Sum $wrapperJarPath" | shasum -a 256 -c > /dev/null 2>&1; then | ||
| wrapperSha256Result=true | ||
| fi | ||
| else | ||
| echo "Checksum validation was requested but neither 'sha256sum' or 'shasum' are available." | ||
| echo "Please install either command, or disable validation by removing 'wrapperSha256Sum' from your maven-wrapper.properties." | ||
| exit 1 | ||
| fi | ||
| if [ $wrapperSha256Result = false ]; then | ||
| echo "Error: Failed to validate Maven wrapper SHA-256, your Maven wrapper might be compromised." >&2 | ||
| echo "Investigate or delete $wrapperJarPath to attempt a clean download." >&2 | ||
| echo "If you updated your Maven version, you need to update the specified wrapperSha256Sum property." >&2 | ||
| exit 1 | ||
| fi | ||
| fi | ||
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| MAVEN_OPTS="$(concat_lines "$MAVEN_PROJECTBASEDIR/.mvn/jvm.config") $MAVEN_OPTS" | ||
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| # For Cygwin, switch paths to Windows format before running java | ||
| if $cygwin; then | ||
| [ -n "$JAVA_HOME" ] && | ||
| JAVA_HOME=$(cygpath --path --windows "$JAVA_HOME") | ||
| [ -n "$CLASSPATH" ] && | ||
| CLASSPATH=$(cygpath --path --windows "$CLASSPATH") | ||
| [ -n "$MAVEN_PROJECTBASEDIR" ] && | ||
| MAVEN_PROJECTBASEDIR=$(cygpath --path --windows "$MAVEN_PROJECTBASEDIR") | ||
| fi | ||
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| # Provide a "standardized" way to retrieve the CLI args that will | ||
| # work with both Windows and non-Windows executions. | ||
| MAVEN_CMD_LINE_ARGS="$MAVEN_CONFIG $*" | ||
| export MAVEN_CMD_LINE_ARGS | ||
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| WRAPPER_LAUNCHER=org.apache.maven.wrapper.MavenWrapperMain | ||
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| # shellcheck disable=SC2086 # safe args | ||
| exec "$JAVACMD" \ | ||
| $MAVEN_OPTS \ | ||
| $MAVEN_DEBUG_OPTS \ | ||
| -classpath "$MAVEN_PROJECTBASEDIR/.mvn/wrapper/maven-wrapper.jar" \ | ||
| "-Dmaven.multiModuleProjectDirectory=${MAVEN_PROJECTBASEDIR}" \ | ||
| ${WRAPPER_LAUNCHER} $MAVEN_CONFIG "$@" | ||
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There was a problem hiding this comment. not needed, maven wrapper resides on the parent level |
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Readme should follow the pattern template. See here: https://github.com/iluwatar/java-design-patterns/wiki/02.-Pattern-template Check out also the other design pattern readmes for examples.