Docker conatiner: Get passed environment varaible in tomcat spring mvc application

dockerenvironment-variablestomcat

I am trying to deploy a SpringMVC application within a Docker container on top to tomcat8.

My problem is This SpringMVC application receive parameters using following code

String username = System.getProperty("db.username");
String password = System.getProperty("db.password");

I am running Docker container with the following command

docker run -e "db.username=root" -e "db.password=123" -v /home/ubuntu/code:/usr/local/tomcat/webapps -i -t -p 80:8080 tomcat

It starts the tomcat conatiner and try to deploy the application, but it does not work and throw application specifc errors username is empty and password is empty.

System.getProperty is not able to receive the passed environment varaibles.

Important: Please note I cannot change the code, I can only modify the docker related things.

I think there should be a way to transform passed environment variables into Java property (in order for System.getProperties to work)

Best Answer

I solved my problem with the following command, but I will still wait for a better answer to accept.

docker run -v /home/ubuntu/code:/usr/local/tomcat/webapps -e JAVA_OPTS="-Ddb.username=root -Ddb.password=abc123" -it -p 80:8080 tomcat

In above command I am trying to run a tomcat container, I have mounted host directory onto container's tomcat webapps directory.

Then I am passing an environment variable JAVA_OPTS which will set Java properties that I will read in my Java code using System.getProperty("db.username")

Related Solutions

Tomcat – multiple webapps in tomcat — what is the optimal architecture

I've done all that you've mentioned and at this point we've gone a completely different direction. We have a JEos VM image we use with a slimmed down virtualized OS and we clone it for each new application. It isn't the most efficient from a memory/CPU/disk perspective, but saves my sanity from a "which port /directory is everything hooked to".

Basically the SERVER determines which application we're using instead of the port/directory/what have you.

Obviously this doesn't work if all you have is one machine or you're already virtualized. In that case, I'd recommend the common CATALINA_BASE and point each new app to a new CATALINA_HOME. A port numbering convention (go by 10's for example) goes a long way to saving your sanity in this case (trust me).

Nginx – use nginx environment variables within static files that nginx serves

I've been looking into resolving the same issue as the OP and this post came up in Google search, so thought I'd add a potential solution.

This post outlines how you can expose an environment variable within nginx config: https://blog.doismellburning.co.uk/environment-variables-in-nginx-config/

And you can return content without having a file in the file system: Reply with 200 from Nginx config without serving a file

Putting these two things together we end up with the following:

env MY_ENV_VAR;

# Snip

http {
    # Snip

    server {
        # Snip

        location ~ ^/config.js$ {
            add_header Content-Type text/javascript;
            set_by_lua $env_var 'return os.getenv("MY_ENV_VAR")';
            return 200 'const MY_ENV_VAR = \'$env_var\'';
        }
    }
}

This has worked for me in a test environment. It's a little cumbersome (not sure it's better than auto-generating a file on Docker launch that contains the vars you need).

Hope that helps.

Best Answer

Related Solutions

Tomcat – multiple webapps in tomcat — what is the optimal architecture

Nginx – use nginx environment variables within static files that nginx serves

Related Topic