How to expose a port from a Docker Swarm without breaking DNS lookups?
I have a web service running as a Spring Boot application inside a Docker container. The web service accesses an external Cassandra database. The web service is exposed from the Docker container by publishing it's HTTP port (8081). The container images are built with 'openjdk:8-jre-alpine' as the base and the only additional changes are the application JAR and a mount for the configuration file. Docker is installed on an Ubuntu VM running in Azure.
This works great as a plain old container but when I run it as part of a Docker swarm the DNS lookups to find the Cassandra database fail.
I don't have an ops background, and networking has never been my strong point, but I've worked out that Docker changes the '/etc/resolv.conf' file when I expose a port from a container running in a swarm and this breaks DNS lookups.
Here's some code to explain a bit more about my setup.
Dockerfile (simplified for security):
FROM openjdk:8-jre-alpine
WORKDIR /service
COPY ./target/application.jar /service
VOLUME /service/config
CMD java -jar application.jar --spring.config.name=message-processor
Starting a simple container:
docker container run -d --restart=unless-stopped --name message-processor --publish 8081:8081 -v /config/jenkins:/service/config -e SPRING_PROFILES_ACTIVE=jenkins -e SPRING_CONFIG_NAME=message-processor message-processor:jenkins
Starting a Swarm service:
docker service create --replicas 2 --name message-processor --publish 8081:8081 --mount type=bind,source=/config/jenkins,target=/service/config -e SPRING_PROFILES_ACTIVE=jenkins -e SPRING_CONFIG_NAME=message-processor message-processor:jenkins
I won't post the contents of the respoective '/etc/resolve.conf' becuase they contain various IP addresses and domain names. In the working container the 'nameserver' value is the same as the host. In the Swam containers where DNS isn't working the 'nameserver' is set to 127.0.0.11.
I can get DNS to work in the Swarm containers if I manually change '/etc/resolve.conf' but this doesn't seem like the right thing to do.
I've started researching and experimenting with Docker networks but it's slow going and I don't feel I'm making much progress.
networking docker-swarm
asked Nov 13 '18 at 12:03
jafwattjafwatt
9613
add a comment |
I have a web service running as a Spring Boot application inside a Docker container. The web service accesses an external Cassandra database. The web service is exposed from the Docker container by publishing it's HTTP port (8081). The container images are built with 'openjdk:8-jre-alpine' as the base and the only additional changes are the application JAR and a mount for the configuration file. Docker is installed on an Ubuntu VM running in Azure.
This works great as a plain old container but when I run it as part of a Docker swarm the DNS lookups to find the Cassandra database fail.
I don't have an ops background, and networking has never been my strong point, but I've worked out that Docker changes the '/etc/resolv.conf' file when I expose a port from a container running in a swarm and this breaks DNS lookups.
Here's some code to explain a bit more about my setup.
Dockerfile (simplified for security):
FROM openjdk:8-jre-alpine
WORKDIR /service
COPY ./target/application.jar /service
VOLUME /service/config
CMD java -jar application.jar --spring.config.name=message-processor
Starting a simple container:
docker container run -d --restart=unless-stopped --name message-processor --publish 8081:8081 -v /config/jenkins:/service/config -e SPRING_PROFILES_ACTIVE=jenkins -e SPRING_CONFIG_NAME=message-processor message-processor:jenkins
Starting a Swarm service:
docker service create --replicas 2 --name message-processor --publish 8081:8081 --mount type=bind,source=/config/jenkins,target=/service/config -e SPRING_PROFILES_ACTIVE=jenkins -e SPRING_CONFIG_NAME=message-processor message-processor:jenkins
I won't post the contents of the respoective '/etc/resolve.conf' becuase they contain various IP addresses and domain names. In the working container the 'nameserver' value is the same as the host. In the Swam containers where DNS isn't working the 'nameserver' is set to 127.0.0.11.
I can get DNS to work in the Swarm containers if I manually change '/etc/resolve.conf' but this doesn't seem like the right thing to do.
I've started researching and experimenting with Docker networks but it's slow going and I don't feel I'm making much progress.
networking docker-swarm
asked Nov 13 '18 at 12:03
jafwattjafwatt
9613
add a comment |
I have a web service running as a Spring Boot application inside a Docker container. The web service accesses an external Cassandra database. The web service is exposed from the Docker container by publishing it's HTTP port (8081). The container images are built with 'openjdk:8-jre-alpine' as the base and the only additional changes are the application JAR and a mount for the configuration file. Docker is installed on an Ubuntu VM running in Azure.
This works great as a plain old container but when I run it as part of a Docker swarm the DNS lookups to find the Cassandra database fail.
I don't have an ops background, and networking has never been my strong point, but I've worked out that Docker changes the '/etc/resolv.conf' file when I expose a port from a container running in a swarm and this breaks DNS lookups.
Here's some code to explain a bit more about my setup.
Dockerfile (simplified for security):
FROM openjdk:8-jre-alpine
WORKDIR /service
COPY ./target/application.jar /service
VOLUME /service/config
CMD java -jar application.jar --spring.config.name=message-processor
Starting a simple container:
docker container run -d --restart=unless-stopped --name message-processor --publish 8081:8081 -v /config/jenkins:/service/config -e SPRING_PROFILES_ACTIVE=jenkins -e SPRING_CONFIG_NAME=message-processor message-processor:jenkins
Starting a Swarm service:
docker service create --replicas 2 --name message-processor --publish 8081:8081 --mount type=bind,source=/config/jenkins,target=/service/config -e SPRING_PROFILES_ACTIVE=jenkins -e SPRING_CONFIG_NAME=message-processor message-processor:jenkins
I won't post the contents of the respoective '/etc/resolve.conf' becuase they contain various IP addresses and domain names. In the working container the 'nameserver' value is the same as the host. In the Swam containers where DNS isn't working the 'nameserver' is set to 127.0.0.11.
I can get DNS to work in the Swarm containers if I manually change '/etc/resolve.conf' but this doesn't seem like the right thing to do.
I've started researching and experimenting with Docker networks but it's slow going and I don't feel I'm making much progress.
networking docker-swarm
asked Nov 13 '18 at 12:03
jafwattjafwatt
9613
I have a web service running as a Spring Boot application inside a Docker container. The web service accesses an external Cassandra database. The web service is exposed from the Docker container by publishing it's HTTP port (8081). The container images are built with 'openjdk:8-jre-alpine' as the base and the only additional changes are the application JAR and a mount for the configuration file. Docker is installed on an Ubuntu VM running in Azure.
This works great as a plain old container but when I run it as part of a Docker swarm the DNS lookups to find the Cassandra database fail.
I don't have an ops background, and networking has never been my strong point, but I've worked out that Docker changes the '/etc/resolv.conf' file when I expose a port from a container running in a swarm and this breaks DNS lookups.
Here's some code to explain a bit more about my setup.
Dockerfile (simplified for security):
FROM openjdk:8-jre-alpine
WORKDIR /service
COPY ./target/application.jar /service
VOLUME /service/config
CMD java -jar application.jar --spring.config.name=message-processor
Starting a simple container:
docker container run -d --restart=unless-stopped --name message-processor --publish 8081:8081 -v /config/jenkins:/service/config -e SPRING_PROFILES_ACTIVE=jenkins -e SPRING_CONFIG_NAME=message-processor message-processor:jenkins
Starting a Swarm service:
docker service create --replicas 2 --name message-processor --publish 8081:8081 --mount type=bind,source=/config/jenkins,target=/service/config -e SPRING_PROFILES_ACTIVE=jenkins -e SPRING_CONFIG_NAME=message-processor message-processor:jenkins
I won't post the contents of the respoective '/etc/resolve.conf' becuase they contain various IP addresses and domain names. In the working container the 'nameserver' value is the same as the host. In the Swam containers where DNS isn't working the 'nameserver' is set to 127.0.0.11.
I can get DNS to work in the Swarm containers if I manually change '/etc/resolve.conf' but this doesn't seem like the right thing to do.
I've started researching and experimenting with Docker networks but it's slow going and I don't feel I'm making much progress.
networking docker-swarm
networking docker-swarm
asked Nov 13 '18 at 12:03
jafwattjafwatt
9613
asked Nov 13 '18 at 12:03
jafwattjafwatt
9613
asked Nov 13 '18 at 12:03
jafwattjafwatt
9613
asked Nov 13 '18 at 12:03
jafwattjafwatt
9613
asked Nov 13 '18 at 12:03
jafwattjafwatt
9613
9613
add a comment |
add a comment |
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