Setting environment variable during Docker container start (on AWS) - docker

Question

I am trying to pass a variable which fetches an IP address with the following code:
${wget -q -O - http://169.254.169.254/latest/meta-data/local-ipv4}
I have tried setting an entrypoint shell script such as:
#!/bin/sh
export ECS_INSTANCE_IP_ADDRESS=$(wget -q -O - http://169.254.169.254/latest/meta-data/local-ipv4)
java -jar user-service-0.0.1-SNAPSHOT.jar
And my dockerfile looking like:
#############
### build ###
#############
# base image
FROM maven:3.6.2-ibmjava-8-alpine as build
# set working directory
WORKDIR /app
# install and cache app dependencies
COPY . /app
RUN mvn clean package
############
### prod ###
############
# base image
FROM openjdk:8-alpine
# set working directory
WORKDIR /app
# copy entrypoint from the 'build environment'
COPY --from=build /app/entrypoint.sh /app/entrypoint.sh
# copy artifact build from the 'build environment'
COPY --from=build /app/target/user-service-0.0.1-SNAPSHOT.jar /app/user-service-0.0.1-SNAPSHOT.jar
# expose port 8081
EXPOSE 8081
# run entrypoint and set variables
ENTRYPOINT ["/bin/sh", "./entrypoint.sh"]
I need this variable to show up when echoing ECS_INSTANCE_IP_ADDRESS so that it can be loaded by a .properties file which $ECS_INSTANCE_IP_ADDRESS. Whenever I get into /bin/sh of the container and echo the variable it shows up blank. If I do an export on that shell I do get the echo response.
Any ideas? I've tried a bunch of things and can't get the variable to be available on the container.

Answer 1

The standard way to set Environment variables in Docker is Dockerfile or Task definition in case of AWS-ECS.
The current docker-entrypoint will set env for that session only, that is why you got empty value when do ssh, but you can verify it has been in that session but this is not recommended approach in Docker.
You can verify
#!/bin/sh
export ECS_INSTANCE_IP_ADDRESS=$(wget -q -O - http://169.254.169.254/latest/meta-data/local-ipv4)
echo "instance IP is ${ECS_INSTANCE_IP_ADDRESS}"
java -jar user-service-0.0.1-SNAPSHOT.jar
You will be able to see this value but it will not be available in another session.
Another example,
Dockerfile
FROM node:alpine
WORKDIR /app
COPY run.sh run.sh
RUN chmod +X run.sh
ENTRYPOINT ["./run.sh"]
entrypoint
#!/bin/sh
export ECS_INSTANCE_IP_ADDRESS=$(wget -q -O - http://169.254.169.254/latest/meta-data/local-ipv4)
node -e "console.log(process.env.ECS_INSTANCE_IP_ADDRESS)"
You will see the node process is able to process the environment, but if you run a command inside the container it will show undefined.
docker exec -it <container_id> ash -c 'node -e "console.log(process.env.ECS_INSTANCE_IP_ADDRESS)"'
Two Option to deal with ENV,
Pass the IP ENV if you already know the IP, as instance always launches before container, for example
The second option is passing environment variable to a java class in command line or How to pass system properties to a jar file if that seems to work for then you entrypoint will be
java -DECS_INSTANCE_IP_ADDRESS=$(wget -q -O - http://169.254.169.254/latest/meta-data/local-ipv4) -jar myjar.jar

Answer 2

This is how I fixed it, I believe there was also an error on the metadata URL and that could have been the culprit.
Dockerfile:
#############
### build ###
#############
# base image
FROM maven:3.6.2-ibmjava-8-alpine as build
# set working directory
WORKDIR /app
# install and cache app dependencies
COPY . /app
RUN mvn clean package
############
### prod ###
############
# base image
FROM openjdk:8-alpine
RUN apk add jq
# set working directory
WORKDIR /app
# copy entrypoint from the 'build environment'
COPY --from=build /app/entrypoint.sh /app/entrypoint.sh
# copy artifact build from the 'build environment'
COPY --from=build /app/target/user-service-0.0.1-SNAPSHOT.jar /app/user-service-0.0.1-SNAPSHOT.jar
# expose port 8081
EXPOSE 8081
# run entrypoint
ENTRYPOINT ["/bin/sh", "./entrypoint.sh"]
entrypoint.sh
#!/bin/sh
export FARGATE_IP=$(wget -q -O - http://169.254.170.2/v2/metadata | jq -r .Containers[0].Networks[0].IPv4Addresses[0])
echo $FARGATE_IP
java -jar user-service-0.0.1-SNAPSHOT.jar
application-aws.properties (not full file):
eureka.instance.ip-address=${FARGATE_IP}
Eureka is printing a template error on the Eureka status page but microservices do connect and respond to actuator health and swagger-ui from Spring Boot.