Docker is being adopted rapidly. Orchestration platforms like Docker Swarm, Kubernetes, and Amazon ECS make running Dockerized services easier and more resilient by managing orchestration and replication across hosts. But all of that makes monitoring more difficult. How can you reliably monitor a service which is unpredictably shifting from one host to another?

The Datadog Agent can automatically track which services are running where, thanks to its Autodiscovery feature. Autodiscovery lets you define configuration templates for Agent checks and specify which containers each check should apply to.

The Agent enables, disables, and regenerates static check configurations from the templates as containers come and go. When your NGINX container moves from 10.0.0.6 to 10.0.0.17, Autodiscovery helps the Agent update its NGINX check configuration with the new IP address so it can keep collecting NGINX metrics without any action on your part.

Overview

In a traditional non-container environment, Datadog Agent configuration is—like the environment in which it runs—static. The Agent reads check configurations from disk when it starts, and as long as it’s running, it continuously runs every configured check.

The configuration files are static, and any network-related options configured within them serve to identify specific instances of a monitored service, for example: a Redis instance at 10.0.0.61:6379. When an Agent check cannot connect to such a service, metrics are missing until you troubleshoot the issue. The Agent check retries its failed connection attempts until an administrator revives the monitored service or fixes the check’s configuration.

With Autodiscovery enabled, the Agent runs checks differently.

Different configuration

Static configuration files aren’t suitable for checks that collect data from ever-changing network endpoints, so Autodiscovery uses templates for check configuration. In each template, the Agent looks for two template variables—%%host%% and %%port%%—to appear in place of any normally-hardcoded network options. For example: a template for the Agent’s Go Expvar check contains the option expvar_url: http://%%host%%:%%port%%. For containers that have more than one IP address or exposed port, you can direct Autodiscovery to pick the right ones by using template variable indexes.

Because templates don’t identify specific instances of a monitored service—which %%host%%? which %%port%%?—Autodiscovery needs one or more container identifiers for each template so it can determine which IP(s) and port(s) to substitute into the templates. For Docker, container identifiers are image names or container labels.

Finally, Autodiscovery can load check templates from places other than disk. Other possible template sources include key-value stores like Consul, and, when running on Kubernetes, Pod annotations.

Different execution

When the Agent starts with Autodiscovery enabled, it loads check templates from all available template sources—not just one or another—along with the templates’ container identifiers. Unlike in a traditional Agent setup, the Agent doesn’t run all checks all the time; it decides which checks to enable by inspecting all containers running on the same host as the Agent.

As the Agent inspects each running container, it checks if the container matches any of the container identifiers from any loaded templates. For each match, the Agent generates a static check configuration by substituting the matching container’s IP address and port. Then it enables the check using the static configuration.

The Agent watches for Docker events-container creation, destruction, starts, and stops—and enables, disables, and regenerates static check configurations on such events.

How to set it up

Running the Agent container

No matter what container orchestration platform you use, run a single docker-dd-agent container on every host in your cluster first. If you use Kubernetes, see the Kubernetes integration page for instructions on running docker-dd-agent. If you use Amazon ECS, see its integration page.

If you use Docker Swarm, run the following command on one of your manager nodes:

docker service create \
  --name dd-agent \
  --mode global \
  --mount type=bind,source=/var/run/docker.sock,target=/var/run/docker.sock \
  --mount type=bind,source=/proc/,target=/host/proc/,ro=true \
  --mount type=bind,source=/sys/fs/cgroup/,target=/host/sys/fs/cgroup,ro=true \
  -e API_KEY=<YOUR_DATADOG_API_KEY> \
  -e SD_BACKEND=docker \
  gcr.io/datadoghq/docker-dd-agent:latest

Otherwise, see the docker-dd-agent documentation for detailed instructions and a comprehensive list of supported environment variables.

If you want the Agent to auto-discover JMX-based checks:

1. Use the gcr.io/datadoghq/docker-dd-agent:latest-jmx image. This image is based on latest, but it includes a JVM, which the Agent needs in order to run jmxfetch.
2. Pass the environment variable SD_JMX_ENABLE=yes when starting gcr.io/datadoghq/docker-dd-agent:latest-jmx.

Check templates

Each Template Source section below shows a different way to configure check templates and their container identifiers.

Files (auto-conf)

Storing templates as local files doesn’t require an external service or a specific orchestration platform. The downside is that you have to restart your Agent containers each time you change, add, or remove templates.

The Agent looks for Autodiscovery templates in its conf.d/auto_conf directory, which contains default templates for the following checks:

• Apache
• Consul
• CouchDB
• Couchbase
• Elasticsearch
• Etcd
• Kubernetes_state
• Kube_dns
• Kyototycoon
• Memcached
• Redis
• Riak

These templates may suit you in basic cases, but if you need to use custom Agent check configurations—say you want to enable extra check options, use different container identifiers, or use template variable indexing)—you need to write your own auto-conf files. You can provide those in a few ways:

1. Add them to each host that runs docker-dd-agent and mount the directory that contains them into the docker-dd-agent container when starting it
2. Build your own docker image based on docker-dd-agent, adding your custom templates to /etc/dd-agent/conf.d/auto_conf
3. On Kubernetes, add them using ConfigMaps

Apache check

Here’s the apache.yaml template packaged with docker-dd-agent:

docker_images:
  - httpd

init_config:

instances:
  - apache_status_url: http://%%host%%/server-status?auto

It looks like a minimal Apache check configuration, but notice the docker_images option. This required option lets you provide container identifiers. Autodiscovery applies this template to any containers on the same host that run an httpd image.

Any httpd image. Suppose you have one container running library/httpd:latest and another running <YOUR_USERNAME>/httpd:v2. Autodiscovery applies the above template to both containers. When it’s loading auto-conf files, Autodiscovery cannot distinguish between identically-named images from different sources or with different tags, and you have to provide short names for container images, for example: httpd, NOT library/httpd:latest.

If this is too limiting—if you need to apply different check configurations to different containers running the same image—use labels to identify the containers. Label each container differently, then add each label to any template file’s docker_images list (yes, docker_images is where to put any kind of container identifier, not just images).

Key-value store

Autodiscovery can use Consul, etcd, and Zookeeper as template sources. To use a key-value store, you must configure it in datadog.conf or in environment variables passed to the docker-dd-agent container.

Configure in datadog.conf

In the datadog.conf file, set the sd_config_backend, sd_backend_host, and sd_backend_port options to, respectively, the key-value store type-etcd, consul, or zookeeper-and the IP address and port of your key-value store:

# For now only Docker is supported so you just need to un-comment this line.
service_discovery_backend: docker

# Define which key/value store must be used to look for configuration templates.
# Default is etcd. Consul is also supported.
sd_config_backend: etcd

# Settings for connecting to the backend. These are the default, edit them if you run a different config.
sd_backend_host: 127.0.0.1
sd_backend_port: 4001

# By default, the Agent looks for the configuration templates under the
# `/datadog/check_configs` key in the back-end.
# If you wish otherwise, uncomment this option and modify its value.
# sd_template_dir: /datadog/check_configs

# If you Consul store requires token authentication for service discovery, you can define that token here.
# consul_token: f45cbd0b-5022-samp-le00-4eaa7c1f40f1

If you’re using Consul and the Consul cluster requires authentication, set consul_token.

Restart the Agent to apply the configuration change.

Configure in environment variables

If you prefer to use environment variables, pass the same options to the container when starting it:

docker service create \
  --name dd-agent \
  --mode global \
  --mount type=bind,source=/var/run/docker.sock,target=/var/run/docker.sock \
  --mount type=bind,source=/proc/,target=/host/proc/,ro=true \
  --mount type=bind,source=/sys/fs/cgroup/,target=/host/sys/fs/cgroup,ro=true \
  -e API_KEY=<YOUR API KEY> \
  -e SD_BACKEND=docker \
  -e SD_CONFIG_BACKEND=etcd \
  -e SD_BACKEND_HOST=127.0.0.1 \
  -e SD_BACKEND_PORT=4001 \
  gcr.io/datadoghq/docker-dd-agent:latest

Note: The option to enable Autodiscovery is called service_discovery_backend in datadog.conf, but it’s called just SD_BACKEND as an environment variable.

With the key-value store enabled as a template source, the Agent looks for templates under the key /datadog/check_configs. Autodiscovery expects a key-value hierarchy like this:

/datadog/
  check_configs/
    docker_image_1/                 # container identifier, for example, httpd
      - check_names: [<CHECK_NAME>] # for example, apache
      - init_configs: [<INIT_CONFIG>]
      - instances: [<INSTANCE_CONFIG>]
    ...

Each template is a 3-tuple: check name, init_config, and instances. The docker_images option from the previous section, which provided container identifiers to Autodiscovery, is not required here. For key-value stores, container identifiers appear as first-level keys under check_config. (Also note, the file-based template in the previous section didn’t need a check name like this example does; there, the Agent inferred the check name from the file name.)

Apache check

The following etcd commands create an Apache check template equivalent to that from the previous section’s example:

etcdctl mkdir /datadog/check_configs/httpd
etcdctl set /datadog/check_configs/httpd/check_names '["apache"]'
etcdctl set /datadog/check_configs/httpd/init_configs '[{}]'
etcdctl set /datadog/check_configs/httpd/instances '[{"apache_status_url": "http://%%host%%/server-status?auto"}]'

Notice that each of the three values is a list. Autodiscovery assembles list items into check configurations based on shared list indexes. In this case, it composes the first (and only) check configuration from check_names[0], init_configs[0] and instances[0].

Unlike auto-conf files, key-value stores may use the short OR long image name as container identifiers, for example: httpd OR library/httpd:latest. The next example uses a long name.

Apache check with website availability monitoring

The following etcd commands create the same Apache template and add an HTTP check template to monitor whether the website created by the Apache container is available:

etcdctl set /datadog/check_configs/library/httpd:latest/check_names '["apache", "http_check"]'
etcdctl set /datadog/check_configs/library/httpd:latest/init_configs '[{}, {}]'
etcdctl set /datadog/check_configs/library/httpd:latest/instances '[{"apache_status_url": "http://%%host%%/server-status?auto"},{"name": "My service", "url": "http://%%host%%", timeout: 1}]'

Again, the order of each list matters. The Agent can only generate the HTTP check configuration correctly if all parts of its configuration have the same index across the three lists (they do-the index is 1).

Kubernetes Pod annotations

As of version 5.12 of the Datadog Agent, you can store check templates in Kubernetes Pod annotations. With Autodiscovery enabled, the Agent detects if it’s running on Kubernetes and automatically searches all Pod annotations for check templates if so; you don’t need to configure Kubernetes as a template source with SD_CONFIG_BACKEND as you do with key-value stores.

Autodiscovery expects annotations to look like this:

annotations:
  service-discovery.datadoghq.com/<container identifier>.check_names: '[<CHECK_NAME>]'
  service-discovery.datadoghq.com/<container identifier>.init_configs: '[<INIT_CONFIG>]'
  service-discovery.datadoghq.com/<container identifier>.instances: '[<INSTANCE_CONFIG>]'

The format is similar to that for key-value stores. The differences are:

• Annotations must begin with service-discovery.datadoghq.com/ (for key-value stores, the starting indicator is /datadog/check_configs/).
• For Annotations, Autodiscovery identifies containers by name, NOT image (as it does for auto-conf files and key-value stores). That is, it looks to match <container identifier> to .spec.containers[0].name, not .spec.containers[0].image.

If you define your Kubernetes Pods directly (kind: Pod), add each Pod’s annotations directly under its metadata section (see the first example below). If you define Pods indirectly with Replication Controllers, Replica Sets, or Deployments, add Pod annotations under .spec.templates.metadata (see the second example below).

Apache check with website availability monitoring

The following Pod annotation defines two templates-equivalent to those from the end of the previous section-for apache containers:

apiVersion: v1
metadata:
  name: apache
  annotations:
    service-discovery.datadoghq.com/apache.check_names: '["apache","http_check"]'
    service-discovery.datadoghq.com/apache.init_configs: '[{},{}]'
    service-discovery.datadoghq.com/apache.instances: '[{"apache_status_url": "http://%%host%%/server-status?auto"},{"name": "My service", "url": "http://%%host%%", timeout: 1}]'
  labels:
    name: apache
spec:
  containers:
    - name: apache # use this as the container identifier in your annotations
      image: httpd # NOT this
      ports:
        - containerPort: 80

Apache and HTTP checks

If you define pods with Deployments, don’t add template annotations to the Deployment metadata; the Agent doesn’t look there. Add them like this:

apiVersion: apps/v1beta1
metadata: # Don't add templates here
  name: apache-deployment
spec:
  replicas: 2
  template:
    metadata:
      labels:
        name: apache
      annotations:
        service-discovery.datadoghq.com/apache.check_names: '["apache","http_check"]'
        service-discovery.datadoghq.com/apache.init_configs: '[{},{}]'
        service-discovery.datadoghq.com/apache.instances: '[{"apache_status_url": "http://%%host%%/server-status?auto"},{"name": "My service", "url": "http://%%host%%", timeout: 1}]'
    spec:
      containers:
      - name: apache # use this as the container identifier in your annotations
        image: httpd # NOT this
        ports:
        - containerPort: 80

Docker label annotations

Since version 5.17 of the Datadog Agent, you can store check templates in Docker labels. With Autodiscovery enabled, the Agent detects if it’s running on Docker and automatically searches all labels for check templates; you don’t need to configure a template source with SD_CONFIG_BACKEND as you do with key-value stores.

Autodiscovery expects labels to look like these examples, depending on the file type:

Dockerfile

LABEL "com.datadoghq.ad.check_names"='[<CHECK_NAME>]'
LABEL "com.datadoghq.ad.init_configs"='[<INIT_CONFIG>]'
LABEL "com.datadoghq.ad.instances"='[<INSTANCE_CONFIG>]'

docker-compose.yaml

labels:
  com.datadoghq.ad.check_names: '[<CHECK_NAME>]'
  com.datadoghq.ad.init_configs: '[<INIT_CONFIG>]'
  com.datadoghq.ad.instances: '[<INSTANCE_CONFIG>]'

docker run command

-l com.datadoghq.ad.check_names='[<CHECK_NAME>]' -l com.datadoghq.ad.init_configs='[<INIT_CONFIG>]' -l com.datadoghq.ad.instances='[<INSTANCE_CONFIG>]'

NGINX Dockerfile

The following Dockerfile launches an NGINX container with Autodiscovery enabled:

FROM nginx

EXPOSE 8080
COPY nginx.conf /etc/nginx/nginx.conf
LABEL "com.datadoghq.ad.check_names"='["nginx"]'
LABEL "com.datadoghq.ad.init_configs"='[{}]'
LABEL "com.datadoghq.ad.instances"='[{"nginx_status_url": "http://%%host%%:%%port%%/nginx_status"}]'

Reference

Supported template variables

The following template variables are handled by the Agent:

• Container IP: host

  • %%host%%: auto-detect the network. Returns the bridge network IP if present; falls back to the last sorted network’s IP.
  • %%host_<NETWORK NAME>%%: specify the network name to use when attached to multiple networks, for example %%host_bridge%%, %%host_swarm%%, etc; behaves like %%host%% if network name specified was not found.

• Container port: port

  • %%port%%: use the highest exposed port sorted numerically and in ascending order (For example, 8443 for a container that exposes ports 80, 443, and 8443)
  • %%port_0%%: use the first port sorted numerically and in ascending order (for the same container, %%port_0%% refers to port 80, %%port_1%% refers to 443
  • If your target port is constant, Datadog recommends you directly specify it, without using the port variable.

• Container PID: pid (Added in 5.15.x)

  • %%pid%%: retrieves the container process ID as returned by docker inspect --format '{{.State.Pid}}' <CONTAINER>

• Container name: container_name (Added in 5.15.x)

  • %%container_name%%: retrieves the container name.

Labels

You can identify containers by label rather than container name or image. Just label any container com.datadoghq.sd.check.id: <SOME_LABEL>, and then put <SOME_LABEL> anywhere you’d normally put a container name or image. For example, if you label a container com.datadoghq.sd.check.id: special-container, Autodiscovery applies to that container any auto-conf template that contains special-container in its docker_images list.

Autodiscovery can only identify each container by label OR image/name-not both-and labels take precedence. For a container that has a com.datadoghq.sd.check.id: special-nginx label and runs the nginx image, the Agent DOESN’T apply templates that include only nginx as a container identifier.

Template source precedence

If you provide a template for the same check type through multiple template sources, the Agent looks for templates in the following order (using the first one it finds):

• Kubernetes annotations
• Key-value stores
• Files

So if you configure a redisdb template both in Consul and as a file (conf.d/auto_conf/redisdb.yaml), the Agent uses the template from Consul.

Troubleshooting

When you’re not sure if Autodiscovery is loading certain checks you’ve configured, use the Agent’s configcheck init script command. For example, to confirm that your Redis template is being loaded from a Kubernetes annotation—not the default auto_conf/redisdb.yaml file:

# docker exec -it <AGENT_CONTAINER_NAME> /etc/init.d/datadog-agent configcheck
.
..
...
Check "redisdb":
  source --> Kubernetes Pod Annotation
  config --> {'instances': [{u'host': u'10.244.1.32', u'port': u'6379', 'tags': [u'image_name:kubernetes/redis-slave', u'kube_namespace:guestbook', u'app:redis', u'role:slave', u'docker_image:kubernetes/redis-slave:v2', u'image_tag:v2', u'kube_replication_controller:redis-slave']}], 'init_config': {}}

To check whether Autodiscovery is loading JMX-based checks:

# docker exec -it <AGENT_CONTAINER_NAME> cat /opt/datadog-agent/run/jmx_status.yaml
timestamp: 1499296559130
checks:
  failed_checks: {}
  initialized_checks:
    SD-jmx_0:
    - {message: null, service_check_count: 0, status: OK, metric_count: 13, instance_name: SD-jmx_0-10.244.2.45-9010}