The agent can be installed either directly on the host machine or as a container. To install directly on the host machine, run the following command and make sure that you use your own unique DD_API_KEY:

DD_API_KEY=wn5AYlhjRhgn3shcjW14y3yOT09WsF7d bash -c "$(curl -L https://raw.githubusercontent.com/DataDog/dd-agent/master/packaging/datadog-agent/source/install_agent.sh)"

To run the agent as a container, use the following command and again make sure that you use your own DD_API_KEY:

sudo docker run -d --name dd-agent -h `hostname` -v /var/run/docker.sock:/var/run/docker.sock -v /proc/mounts:/host/proc/mounts:ro -v /sys/fs/cgroup/:/host/sys/fs/cgroup:ro -e API_KEY=wn5AYlhjRhgn3shcjW14y3yOT09WsF7d datadog/docker-dd-agent

Once the agent has been installed, it will call back to Datadog and the host will appear in your account.

If the agent has been installed directly on the host machine then we will need to enable the Docker integration, if you installed the agent using the container then this will have been done for you automatically.

To do this, you first need to allow the Datadog agent access to your Docker installation by adding the dd-agent user to the Docker group by running the following command:

usermod -a -G docker dd-agent

The next step is to create the docker.yaml configuration file, luckily the Datadog agent ships with an example configuration file that we can use; copy this in place and then restart the agent:

cp -pr /etc/dd-agent/conf.d/docker.yaml.example /etc/dd-agent/conf.d/docker.yaml
sudo /etc/init.d/datadog-agent restart

Now the agent on our host machine has been configured and the final step is to enable the integration through the website. To do this, go to https://app.datadoghq.com/ and click on Integrations, scroll down and then click on install on Docker:

Once you click install, you will be presented with an overview of the integration, click on the Configuration tab, this gives instructions on how to configure the agent; as we have already done this step, you can click on Install Integration.

You can find more information on installing the agent and the integrations at the following URLs:

Now, you have installed the agent and enabled the Docker integration, you can start to have a look around the web interface. To find your host, click on "Infrastructure" in the left-hand side menu.

You should be taken to a screen that contains a map of your infrastructure. Like me, you probably only have a single host machine listed, click on it and some basic stats should appear at the bottom of the screen:

If you don't already have the containers launched, now would be a good time to do so, lets launch the WordPress installation again using:

sudo su -
mkdir ~/wordpress
curl -L https://raw.githubusercontent.com/russmckendrick/monitoring-docker/master/chapter05/wordpress/docker-compose.yml > ~/wordpress/docker-compose.yml
cd ~/wordpress
docker-compose up -d

Now, go back to the web interface, from there you can click on any of the services listed on the hexagon. This will bring up some basic metrics for the service you have selected. If you click on docker, you will see a link for a Docker Dashboard among the various graphs and so on; clicking this will take you to a more detailed view of your containers:

As you can see, this gives us our now familiar break down of the CPU and memory metrics, along with in the top right of the dashboard a breakdown of the container activity on the host machine; this logs events, such as stopping and starting containers.

Datadog currently records the following metrics:

From the Metrics explorer option in the left-hand side menu, you can start to graph these metrics and once you have the graphs, you can then start to add them to your own custom dashboards or even annotate them. When you annotate a graph, a snapshot is created and the graph shows up in the events queue along with the other events, that have been recorded, such as container stopping and starting:

Also, within the web interface you can configure monitors; these allow you to define triggers, which alert you if your conditions are not met. Alerts can be sent as e-mails or via third party services, such as Slack, Campfire, or PagerDuty.

While Datadog's Docker integration only gives you the basic metrics on your containers, it does have a wealth of features and integration with other applications and third parties. If you need to monitor a number of different services alongside your Docker containers, then this service could be for you: