Docker is the world’s leading software container platform. Developers use Docker to eliminate “works on my machine” problems when collaborating on code with co-workers. Operators use Docker to run and manage apps side-by-side in isolated containers to get better compute density. Enterprises use Docker to build agile software delivery pipelines to ship new features faster, more securely and with confidence for both Linux, Windows Server, and Linux-on-mainframe apps.


To maintain a high level of stability, reliability, and support, our Elastic Docker images are based on the Docker images provided by Their Docker images are built on CentOS 7:

To leverage a common core OS layer, all of our Docker images are then built on CentOS 7.


In the current Security Onion 16.04 platform, only a few of the components are delivered via containers. The remaining components (including the configuration files for those containers) are delivered via Ubuntu packages.



If you have multiple instances of Docker running in your environment (e.g., multiple physical or virtual machines, all running the Docker daemon), each time one of them requires an image that it doesn’t have it will go out to the internet and fetch it from the public Docker registry. By running a local registry mirror, you can keep most of the redundant image fetch traffic on your local network.

We can leverage the Docker registry (as a pull-through cache) with our Security Onion Docker images. As mentioned above, this will allow us to cut down on external requests and bandwidth, cache the images on a local server, and only pull new images when they are available.

We can easily configure our Security Onion master server and sensor by running the following script on each machine (watch out for line-wrapping) :

sudo bash so-docker-registry

The above script:

  • Sets up a Docker container named docker-registry on the master server - this container exposes port 5000 for (only locally).
  • Configures the master server to use the docker-registry container as its proxy to pull images (registry-mirror in /etc/default/docker).
  • Configures a sensor to use to docker-registry on the master server as a proxy to pull images – this is done through the addition of a local port forward (5000) through the existing autossh tunnel (/root/.ssh/securityonion_ssh.conf), and setting the registry-mirror value for the docker client on the sensor (/etc/default/docker)
  • Restarts Security Onion Docker containers so the latest images are cached on the master and pulled to the sensor.

After the script has completed (after running on both machines), the newest images from the securityonionsolutions repo should be locally cached on the master, and already pulled to the sensor.

We can check this by running the following from the master (or sensor):

curl localhost:5000/v2/_catalog

From here on, whenever soup checks for new images, it will pull them from the master server instead of Docker Hub.

Sneakernet Updates

If we need to perform offline updates of Docker images, we can do so by cloning the security-onion-docker-airgap script(s) at

git clone
cd securityonion-docker-airgap

The script(s) should be run first on a machine with internet access – Docker images will be downloaded and saved to a single images.tar file.

sudo ./so-elastic-airgap

Choose the Save option.

From there, the securityonion-docker-airgap directory (including the images.tar file) should be copied to the destination machine.

Once there, change into the securityonion-docker-airgap directory:

cd securityonion-docker-airgap

Run the so-elastic-airgap script, and choose the Load option.

The Docker images should now be loaded. We can verify this by running:

sudo docker images



By default, Docker configures it’s bridge with an IP of

For many folks this is fine, but what if we actually use the the range within our internal network(s)? This results in a conflict when trying to assign IP addresses to interfaces and trying to route outside of the host.

A simple solution to this is to do the following:

Create the following file - /etc/docker/daemon.json.
Inside of the file, place the following:
  "bip": "your_docker_bridge_ip/netmask"

Restart Docker:

sudo service docker restart

Running netstat -rn should show that the range for the docker0 bridge has changed.


Our Docker containers all belong to a common Docker bridge network, called so-elastic-net. Each container is also aliased, so that communication can occur between the different docker containers using said alias. For example, communication to the so-elasticsearch container would occur through an alias of elasticsearch.

You may come across interfaces in ifconfig with the format veth*. These are the external interfaces for each of the Docker containers. These interfaces correspond to internal Docker container interfaces (within the Docker container itself).

To identify which external interface belongs to which container, we can do something like the following:

From the host, type:

sudo docker exec so-elasticsearch cat /sys/class/net/eth0/iflink

This should provide you with a value with which you can grep the host net class ifindex(es):

grep 25 /sys/class/net/veth*/ifindex | cut -d'/' -f5

You should then receive some output similar to the following:


where vethc5ff027 is the external interface of eth0 within the so-elasticsearch container.


Our Docker images are stored on Docker Hub:

If you download our Security Onion ISO image, the Docker engine and these Docker images are baked right into the ISO image.

If you instead use another ISO image, you will install the securityonion-elastic package and will then run sudo so-elastic-download which will install the Docker engine and then download the Docker images from Docker Hub.


Our soup utility for installing updates now includes support for updating Docker images.


To prevent tampering, our Docker images are signed using Docker Notary:

Any time we push an image to Docker Hub, we explicitly set --disable-content-trust=false to sign the image using Docker Notary.

Any time we download an image from Docker Hub, we also explicitly set --disable-content-trust=false to verify that signature using Docker Notary.

VMware Tools

If you have VMware Tools installed and you suspend and then resume, the Docker interfaces will no longer have IP addresses and the Elastic stack will no longer be able to communicate. One workaround is to remove /etc/vmware-tools/scripts/vmware/network to prevent VMware suspend/resume from modifying your network configuration.