Configuring Docker Flow Monitor

Docker Flow Monitor can be configured through Docker environment variables and/or by creating a new image based on dockerflow/docker-flow-monitor.

Startup Arguments

Environment variables prefixed will ARG_ are used instead Prometheus startup arguments.

The formatting rules for the ARG variables are as follows:

  1. Variable name has to be prefixed with ARG_.
  2. Underscores (_) will be replaced with dots (.).
  3. Capital letters will be transformed to lower case.

For example, if environment variables ARG_WEB_ROUTE-PREFIX=/monitor and ARG_WEB_EXTERNAL-URL=http://localhost/monitor are defined, Prometheus will be started with the arguments web.route-prefix=/monitor and web.external-url=http://localhost/monitor. The result would be Prometheus initialization equivalent to the command that follows.

prometheus --web.route-prefix=/monitor --web.external-url=http://localhost/monitor

ARG variables defined by default are as follows.


The ARG_ALERTMANAGER_URL environment variable accepts a comma separated list of alertmanagers:


These urls are configured in Prometheus's config file as static_configs:

  - static_configs:
    - targets:
      - alert-manager:9093
      - alert-manager2:9093
    scheme: http


Environment variables prefixed with GLOBAL__, ALERTING__, SCRAPE_CONFIGS__, REMOTE_WRITE__, and REMOTE_READ__ are used to configure Prometheus.

The formatting rules for these variable are as follows:

  1. Environment keys will be transformed to lowercase.
  2. Double underscore is used to go one level deeper in a yaml dictionary.
  3. A single underscore followed by a number indicates the position of an array.


The following are examples of using environmental variables to configure Prometheus. Pleaes consult the Prometheus configuration documentation for all configuration options.

  scrape_interval: 10s
  • GLOBAL__EXTERNAL_LABELS=cluster=swarm
    cluster: swarm
    type: production

This is NOT GLOBAL__EXTERNAL_LABELS__CLUSTER=swarm because CLUSTER is not a standard Prometheus configuration. The external_labels option is a list of key values as shown in their documentation:

  [ <labelname>: <labelvalue> ... ]
  • REMOTE_WRITE_1__URL=http://first.acme.com/write, REMOTE_WRITE_1__REMOTE_TIMEOUT=10s, REMOTE_WRITE_2__URL=http://second.acme.com/write
- url: http://acme.com/write
  remote_timeout: 30s
- url: http://second.acme.com/write

Trailing numbers in the REMOTE_WRITE_1 and REMOTE_WRITE_2 prefixes dictates the position of the array of dictionaries.

- write_relabel_configs:
  - source_labels: [label1]

Scrape Environment Configuration

It is possible to add servers that are not part of the Docker Swarm Cluster just adding the variables SCRAPE_PORT and SERVICE_NAME on the environment. The project is going to use the static_configs configuration.


You can also add a service via api using the reconfigure entry point.

curl `[IP_OF_ONE_OF_SWARM_NODES]:8080/v1/docker-flow-monitor/reconfigure?scrapePort=[PORT]&serviceName=[IP_OR_DOMAIN]&scrapeType=static_configs

Please consult Prometheus Configuration for more information about the available options.

Scrape Secret Configuration

Additional scrapes can be added through files prefixed with scrape_. By default, all such files located in /run/secrets are automatically added to the scrape_configs section of the configuration. The directory can be changed by setting a different value to the environment variable CONFIGS_DIR.

The simplest way to add scrape configs is to use Docker secrets or configs.

Scrape Label Configuration With Service and Node Labels

When using a version of Docker Flow Swarm Listener, DFSL, newer than 18.03.20-39, you can configure DFSL to send node information to Docker Flow Monitor, DFM. This can be done by setting DF_INCLUDE_NODE_IP_INFO to true in the DFSL environment. DFM will automatically display the node hostnames as a label for each prometheus target. The DF_SCRAPE_TARGET_LABELS env variable allows for additional labels to be displayed.

In addition to service labels, DFM can be configured to import node and engine labels prefixed with com.df. as prometheus labels for our targets. First, configure DFSL to push node events to DFM by setting the following environment variables in DFSL:

  1. DF_NOTIFY_CREATE_NODE_URL=[MONITOR_DNS]:[MONITOR_PORT]/v1/docker-flow-monitor/node/reconfigure
  2. DF_NOTIFY_REMOVE_NODE_URL=[MONITOR_DNS]:[MONITOR_PORT]/v1/docker-flow-monitor/node/remove

Next set the following environment variables in DFM:

  1. DF_GET_NODES_URL=[SWARM_LISTENER_DNS]:[SWARM_LISTENER_PORT]/v1/docker-flow-swarm-listener/get-nodes
  2. DF_NODE_TARGET_LABELS to a comma seperate list of labels use.


Only [a-zA-Z0-9_] are valid characters in prometheus labels in DF_NODE_TARGET_LABELS and DF_SCRAPE_TARGET_LABELS.

For example, the stack file, stacks/docker-flow-monitor-flexible-labels.yml, configures DFM and DFSL to use service and node labels as prometheus labels. The swarm-listener service is defined as follows:

    image: vfarcic/docker-flow-swarm-listener
      - DF_NOTIFY_CREATE_SERVICE_URL=http://monitor:8080/v1/docker-flow-monitor/reconfigure
      - DF_NOTIFY_REMOVE_SERVICE_URL=http://monitor:8080/v1/docker-flow-monitor/remove
      - DF_NOTIFY_CREATE_NODE_URL=http://monitor:8080/v1/docker-flow-monitor/node/reconfigure
      - DF_NOTIFY_REMOVE_NODE_URL=http://monitor:8080/v1/docker-flow-monitor/node/remove

The DF_NOTIFY_* environment variables defined in swarm-listener configures it to send service and node notifications to the monitor service. Setting DF_INCLUDE_NODE_IP_INFO to true configures swarm-listener to send node information for service changes.

The monitor service is defined as follows:

    image: dockerflow/docker-flow-monitor:${TAG:-latest}
      - DF_SCRAPE_TARGET_LABELS=env,metricType
      - DF_NODE_TARGET_LABELS=aws_region,role
      - DF_GET_NODES_URL=http://swarm-listener:8080/v1/docker-flow-swarm-listener/get-nodes

The environment variable DF_GET_NODES_URL configures monitor to query swarm-listener for all nodes during startup. DF_SCRAPE_TARGET_LABELS=env,metricType configures monitor to use service labels com.df.env and com.df.metricType as prometheus labels with the com.df. prefix removed: env and metricType respectively. DF_NODE_TARGET_LABELS=aws_region,role configures monitor to use node label com.df.aws_region as a prometheus label with com.df. prefix remove: aws_region. The role target label is used by DFSL to denote the role of the node: manager and worker. For a complete list of node labels used by DFSL, head over to the Docker Flow Swarm Listener Usage Docs.

For more information, please visit the Flexible Labeling Tutorial to learn more about this feature!