How to monitor java application on Docker

In this simple guide, we will show you how to Install JENNIFER agent and monitor you java application running on docker container.

1- Requirements

• JENNIFER Java Agent Installation Package.

2- Steps Summary

• Download JENNIFER agent package
• Move the package to the root of your working directory where you have your Dockerfile.
• Copy the installation package to the container and extract it
• Copy the agent configuration file to the container
• update the application server startup script to install the agent

3- Details

In this tutorial, we will be using tomcat as our application server. Before we get the configuration. Make sure to download the agent package and add it to your project root where you have your Docker file. 

After downloading the agent package, move it to your working directory where you have your Dockerfile. Also create 2 files, jennifer.conf and setenv.sh in the same directory. Your working directory should look like the following.

??? java_agent_install
    ??? Dockerfile
    ??? jennifer-agent-java-x.x.x.x.zip
    ??? jennifer.conf
    ??? setenv.sh

• jennifer.conf: We will use this file as our agent configuration file
• setenv.sh: The setenv.sh file will be used to set JENNIFER agent JVM arguments.

3.1 Agent Configurations

We will start by modifying the agent configuration file. Open the jennifer.conf file and modify the server_address value to point to your JENNIFER Data server IP. Also, modify the server_port and domain_id values if you are not using the default values. The agent configuration file should look like this

server_address = 192.168.9.37
server_port = 5000

# default log_dir "{agent_home}/logs"
# log_dir = {agent_home}/logs
# log_file =
# log_level : 1(info), 2(debug), 3(trace)
log_level = 1
log_encoding = UTF-8
log_rotation = true
# log_max_age : Working when log_rotation is activated. Valid ragne is (1-365)
# log_max_age = 0

# domain_id : Valid range is (1-32767)
domain_id = 1000

3.2 Tomcat configurations

The next step is to modify setenv.sh file. Open this file with your editor and set CATALINA_OPTS value.

# JENNIFER Java Agent
AGENT_HOME=/opt/agent.java
export CATALINA_OPTS="$CATALINA_OPTS -javaagent:$AGENT_HOME/jennifer.jar -Djennifer.config=$AGENT_HOME/conf/jennifer.conf"

3.3 Docker file. 

The last thing to do is to work on our docker file. The steps needed to install the agent are :

1. Copy the zip file to the container and extract it to /opt/agent.java directory
2. Copy the jennifer.conf to the agent conf directory
3. Copy setenv.sh to CATALINA_HOME/bin directory

Our Dockerfile looks like the following

FROM alpine AS builder

LABEL maintainer="Khalid Saeed khalid@jennifersoft.com"
ENV AGENT_VERSION=5.3.2.7

RUN apk --no-cache add unzip

COPY jennifer-agent-java-${AGENT_VERSION}.zip /
RUN unzip -oq jennifer-agent-java-${AGENT_VERSION}.zip -d /tmp


FROM tomcat:8.5-jre8-alpine

RUN apk update && apk upgrade

COPY --from=builder /tmp/agent.java /opt/agent.java
COPY jennifer.conf /opt/agent.java/conf/jennifer.conf
COPY setenv.sh ${CATALINA_HOME}/bin

In this example, we are using multi-stage builder. However, you can create the Dockerfile in any way you see feet. 

After creating the docker file you can build and run the container

docker build -t jennifer-java .
docker run -d --name test jennifer-java

If you followed the steps correctly, you should see the agent appearing on your JENNIFER dashboard

Example Code

You can find an example code at this Github repo