Monitor a dokku server with Prometheus, Grafana & Loki

Posted on: Thursday, 14 January 2021

This post outlines how I set up a full monitoring stack on my single dokku server. While it's a pretty long post, it's not very detailed and just covers the absolute basics of setting up the various services. I will update this post over time with any improvements I make to my stack.

Services Overview

We'll set up 6 different services as dokku apps:

  • prometheus - monitoring and alerting toolkit
  • loki - application logs indexer
  • promtail - ships the contents of local logs to loki
  • grafana - read & graph time series data from loki & prometheus
  • node-exporter - provides metrics about the host machine
  • cadvisor - provides metrics about running docker containers


You'll need dokku installed on a single server running Ubuntu 20.04. I've tested these instructions on dokku version v0.22.8, but they'll probably work on other versions too.

Public endpoints are secured with http-auth and tls so you'll need to make sure you have the relevant plugins installed:

dokku plugin:install
dokku plugin:install

Adding a full monitoring solution increases the required resources for your server, but once the tools are set up you'll have metrics to identify whether you need any additional resources.


We'll use a private docker network to allow the apps to communicate with each other in a private network.

Create a bridged network called prometheus-bridge:

dokku network:create prometheus-bridge

Set up Prometheus

Create the prometheus dokku app and set the ports:

dokku apps:create prometheus
dokku proxy:ports-add prometheus http:80:9090

Set the volume mounts for persistent storage:

mkdir -p /var/lib/dokku/data/storage/prometheus/{config,data}
touch /var/lib/dokku/data/storage/prometheus/config/{alert.rules,prometheus.yml}
chown -R nobody:nogroup /var/lib/dokku/data/storage/prometheus

dokku storage:mount prometheus /var/lib/dokku/data/storage/prometheus/config:/etc/prometheus
dokku storage:mount prometheus /var/lib/dokku/data/storage/prometheus/data:/prometheus

Set prometheus config:

dokku config:set --no-restart prometheus DOKKU_DOCKERFILE_START_CMD="--config.file=/etc/prometheus/prometheus.yml

(We set to prevent tsdb from creating a lockfile to allow us to re-deploy without data read errors.)

Attach prometheus to the prometheus-bridge network:

dokku network:set prometheus attach-post-deploy prometheus-bridge

Prometheus Config

Create the config file at location /var/lib/dokku/data/storage/prometheus/config/prometheus.yml:

  scrape_interval: 15s

  - job_name: 'prometheus'
    scrape_interval: 15s
      - targets:
          - 'localhost:9090'
  - job_name: node-exporter
    scrape_interval: 15s
    scheme: https
      username: <username>
      password: <password>
      - targets:
          - ''
  - job_name: cadvisor
    scrape_interval: 15s
    scheme: http
      - targets:
          - 'cadvisor.web:8080'

Ideally we only want to use local hostnames available within the private prometheus-bridge network, but we have to use a public endpoint for node-exporter as it's using the host network and cannot be attached to the prometheus-bridge network.

Deploy Prometheus

Deploy the prometheus app and secure it with http-auth:

docker pull prom/prometheus:latest
docker tag prom/prometheus:latest dokku/prometheus:latest
dokku tags:deploy prometheus latest

dokku letsencrypt prometheus
dokku http-auth:on prometheus USER PASSWORD

Visit to confirm prometheus can connect to localhost (and other targets should all be down).

Set up Node-exporter

Node exporter provides metrics on the host machine.

Create the app and set the config:

dokku apps:create node-exporter
dokku proxy:ports-set node-exporter http:80:9100
dokku config:set --no-restart node-exporter DOKKU_DOCKERFILE_START_CMD=" --path.procfs=/host/proc --path.sysfs=/host/sys"

Set the storage mounts:

mkdir -p /var/lib/dokku/data/storage/node-exporter
chown nobody:nogroup /var/lib/dokku/data/storage/node-exporter

dokku storage:mount node-exporter /proc:/host/proc:ro
dokku storage:mount node-exporter /:/rootfs:ro
dokku storage:mount node-exporter /sys:/host/sys:ro
dokku storage:mount node-exporter /var/lib/dokku/data/storage/node-exporter:/data

Add node-exporter to the host network:

dokku docker-options:add node-exporter deploy "--net=host"

Disable zero-downtime checks:

dokku checks:disable node-exporter

Deploy the app:

docker image pull prom/node-exporter:latest
docker image tag prom/node-exporter:latest dokku/node-exporter:latest

dokku tags:deploy node-exporter latest
dokku letsencrypt node-exporter
dokku http-auth:on node-exporter <username> <password>

Set up cAdvisor

Create the app and set the config:

dokku apps:create cadvisor
dokku proxy:ports-set cadvisor http:80:8080
dokku config:set --no-restart cadvisor DOKKU_DOCKERFILE_START_CMD="--docker_only --housekeeping_interval=10s --max_housekeeping_interval=60s"

Set the storage mounts:

dokku storage:mount cadvisor /:/rootfs:ro
dokku storage:mount cadvisor /sys:/sys:ro
dokku storage:mount cadvisor /var/lib/docker:/var/lib/docker:ro
dokku storage:mount cadvisor /var/run:/var/run:rw

Attach to the prometheus-bridge network:

dokku network:set cadvisor attach-post-deploy prometheus-bridge

Deploy the app:

docker image pull
docker image tag dokku/cadvisor:latest

dokku tags:deploy cadvisor latest
dokku letsencrypt cadvisor
dokku http-auth:on cadvisor <username> <password>

Set up loki

Create the app and set the config:

dokku apps:create loki
dokku proxy:ports-add loki http:80:3100
dokku config:set --no-restart loki DOKKU_DOCKERFILE_START_CMD="-config.file=/etc/loki/loki-config.yaml"

Set the storage mounts:

mkdir -p /var/lib/dokku/data/storage/loki/config
touch /var/lib/dokku/data/storage/loki/config/loki-config.yml
chown -R nobody:nogroup /var/lib/dokku/data/storage/loki
dokku storage:mount loki /var/lib/dokku/data/storage/loki/config:/etc/loki

Attach to the prometheus-bridge network:

dokku network:set loki attach-post-deploy prometheus-bridge

Loki Config

Create the configuration file at location /var/lib/dokku/data/storage/loki/config/loki-config.yaml:

auth_enabled: false

  http_listen_port: 3100

        store: inmemory
      replication_factor: 1
    final_sleep: 0s
  chunk_idle_period: 1h # Any chunk not receiving new logs in this time will be flushed
  max_chunk_age: 1h # All chunks will be flushed when they hit this age, default is 1h
  chunk_target_size: 1048576 # Loki will attempt to build chunks up to 1.5MB, flushing first if chunk_idle_period or max_chunk_age is reached first
  chunk_retain_period: 30s # Must be greater than index read cache TTL if using an index cache (Default index read cache TTL is 5m)
  max_transfer_retries: 0 # Chunk transfers disabled

    - from: 2020-10-24
      store: boltdb-shipper
      object_store: filesystem
      schema: v11
        prefix: index_
        period: 24h

    active_index_directory: /tmp/loki/boltdb-shipper-active
    cache_location: /tmp/loki/boltdb-shipper-cache
    cache_ttl: 24h # Can be increased for faster performance over longer query periods, uses more disk space
    shared_store: filesystem
    directory: /tmp/loki/chunks

  working_directory: /tmp/loki/boltdb-shipper-compactor
  shared_store: filesystem

  reject_old_samples: true
  reject_old_samples_max_age: 168h

  max_look_back_period: 0s

  retention_deletes_enabled: false
  retention_period: 0s

    type: local
      directory: /tmp/loki/rules
  rule_path: /tmp/loki/rules-temp
  alertmanager_url: http://localhost:9093
      store: inmemory
  enable_api: true

Deploy loki

docker image pull grafana/loki:2.0.0
docker image tag grafana/loki:2.0.0 dokku/loki:latest
dokku tags:deploy loki latest
dokku letsencrypt loki
dokku http-auth:on loki <username> <password>

The following endpoints should be available:

Set up Promtail

Promtail will read logs and push to loki.

Create the app and set the config:

dokku apps:create promtail
dokku config:set --no-restart promtail DOKKU_DOCKERFILE_START_CMD="-config.file=/etc/promtail/promtail-config.yaml"

Set the storage mounts:

mkdir -p /var/lib/dokku/data/storage/promtail/config
touch /var/lib/dokku/data/storage/promtail/config/promtail-config.yml
chown -R nobody:nogroup /var/lib/dokku/data/storage/promtail
dokku storage:mount promtail /var/lib/dokku/data/storage/promtail/config:/etc/promtail
dokku storage:mount promtail /var/log:/var/log

Attach to the prometheus-bridge network:

dokku network:set promtail attach-post-deploy prometheus-bridge

Promtail Config

Create the configuration file at location /var/lib/dokku/data/storage/promtail/config/promtail-config.yaml.

  http_listen_port: 9080
  grpc_listen_port: 0

  filename: /tmp/positions.yaml

  - url: http://loki.web:3100/loki/api/v1/push

  - job_name: system
      - targets:
          - localhost
          job: varlogs
          __path__: /var/log/*log
      - targets:
          - localhost
          job: nginx
          __path__: /var/log/nginx/*log

Deploy promtail

docker image pull grafana/promtail:2.0.0
docker image tag grafana/promtail:2.0.0 dokku/promtail:latest
dokku tags:deploy promtail latest
dokku domains:disable promtail

Set up Grafana

Create the dokku app and set the ports:

dokku apps:create grafana
dokku proxy:ports-add grafana http:80:3000

Mount the data & config directories:

mkdir -p /var/lib/dokku/data/storage/grafana/{config,data,plugins}
mkdir -p /var/lib/dokku/data/storage/grafana/config/provisioning/datasources
chown -R 472:472 /var/lib/dokku/data/storage/grafana

dokku storage:mount grafana /var/lib/dokku/data/storage/grafana/config/provisioning/datasources:/etc/grafana/provisioning/datasources
dokku storage:mount grafana /var/lib/dokku/data/storage/grafana/data:/var/lib/grafana
dokku storage:mount grafana /var/lib/dokku/data/storage/grafana/plugins:/var/lib/grafana/plugins

Set the prometheus data source in /var/lib/dokku/data/storage/grafana/config/provisioning/datasources/prometheus.yml:

  - name: Prometheus
    type: prometheus
    access: proxy
    orgId: 1
    url: http://prometheus.web:9090
    basicAuth: false
    isDefault: true
    version: 1
    editable: true

Set the loki data source in /var/lib/dokku/data/storage/grafana/config/provisioning/datasources/loki.yml:

  - name: Loki
    type: loki
    access: proxy
    orgId: 1
    url: http://loki.web:3100
    basicAuth: false
    isDefault: false
    version: 1
    editable: true

Attach to the prometheus-bridge network:

dokku network:set grafana attach-post-deploy prometheus-bridge

Add the WorldMap plugin (required for the web-analytics dashboard):

apt-get install -y unzip
curl -o -L
unzip -d /var/lib/dokku/data/storage/grafana/plugins/
rm -f

Deploy Grafana:

docker pull grafana/grafana:latest
docker tag grafana/grafana:latest dokku/grafana:latest
dokku tags:deploy grafana latest
dokku letsencrypt grafana

Data sources

By default the following data sources should be enabled:

  • http://prometheus.web:9090
  • http://loki.web:3100

To explore the loki logs, click Explore on the sidebar, select the Loki datasource in the top-left dropdown, and then choose a log stream using the Log labels button.

Monitor Nginx Access Logs

We can use loki and promtail to index the dokku nginx reverse proxy access logs and display them as metrics in grafana. To do this we need to configure nginx to output logs in a particular format and enable the geoip2 module to map ip addresses to locations.

Configure Nginx

Install the maxmind tools:

add-apt-repository -y ppa:maxmind/ppa
apt-get update
apt-get install -y geoipupdate libmaxminddb0 libmaxminddb-dev mmdb-bin

Download geoip Database

Sign up for GeoLite2 (it's free) and create a new license key.

Update /etc/GeoIP.conf:

EditionIDs GeoLite2-City GeoLite2-Country

Update the geoip database:


List the geoip databases:

ls -l /usr/share/GeoIP/

You should see both the Country and City databases:


Install the Nginx geoip2 Module

Adding new modules to nginx requires you to build from source but Ubuntu 20.04 ships with a package called nginx-full with the mod-http-geoip2 module enabled (amongst others). For convenience we'll use this package and disable the dynamic modules we don't need.

Install nginx-full:

apt-get install -y nginx-full

Inspect the configure arguments to confirm support for the http-geoip2 module is enabled:

nginx -V

You should see something like:


Disable the modules we don't need:

rm /etc/nginx/modules-enabled/50-mod-http-auth-pam.conf
rm /etc/nginx/modules-enabled/50-mod-http-dav-ext.conf
rm /etc/nginx/modules-enabled/50-mod-http-echo.conf
rm /etc/nginx/modules-enabled/50-mod-http-geoip.conf
rm /etc/nginx/modules-enabled/50-mod-http-subs-filter.conf
rm /etc/nginx/modules-enabled/50-mod-http-upstream-fair.conf

List the enabled modules:

ls -l /etc/nginx/modules-enabled

You should see:

50-mod-http-geoip2.conf -> /usr/share/nginx/modules-available/mod-http-geoip2.conf
50-mod-http-image-filter.conf -> /usr/share/nginx/modules-available/mod-http-image-filter.conf
50-mod-http-xslt-filter.conf -> /usr/share/nginx/modules-available/mod-http-xslt-filter.conf
50-mod-mail.conf -> /usr/share/nginx/modules-available/mod-mail.conf
50-mod-stream.conf -> /usr/share/nginx/modules-available/mod-stream.conf

Update /etc/nginx/nginx.conf to load the geoip databases:

http {

    geoip2 /usr/share/GeoIP/GeoLite2-Country.mmdb {
        auto_reload 60m;
        $geoip2_metadata_country_build metadata build_epoch;
        $geoip2_data_country_code country iso_code;
        $geoip2_data_country_name country names en;

    geoip2 /usr/share/GeoIP/GeoLite2-City.mmdb {
        auto_reload 60m;
        $geoip2_metadata_city_build metadata build_epoch;
        $geoip2_data_city_name city names en;


Restart nginx:

nginx -t
service nginx reload

Update Application Log Format

Update your app nginx configuration capture additional metrics and store in json format.

For example in file /home/dokku/my-app/nginx.conf:

log_format json_analytics escape=json '{'
  '"msec": "$msec", ' # request unixtime in seconds with a milliseconds resolution
  '"connection": "$connection", ' # connection serial number
  '"connection_requests": "$connection_requests", ' # number of requests made in connection
  '"pid": "$pid", ' # process pid
  '"request_id": "$request_id", ' # the unique request id
  '"request_length": "$request_length", ' # request length (including headers and body)
  '"remote_addr": "$remote_addr", ' # client IP
  '"remote_user": "$remote_user", ' # client HTTP username
  '"remote_port": "$remote_port", ' # client port
  '"time_local": "$time_local", '
  '"time_iso8601": "$time_iso8601", ' # local time in the ISO 8601 standard format
  '"request": "$request", ' # full path no arguments if the request
  '"request_uri": "$request_uri", ' # full path and arguments if the request
  '"args": "$args", ' # args
  '"status": "$status", ' # response status code
  '"body_bytes_sent": "$body_bytes_sent", ' # the number of body bytes exclude headers sent to a client
  '"bytes_sent": "$bytes_sent", ' # the number of bytes sent to a client
  '"http_referer": "$http_referer", ' # HTTP referer
  '"http_user_agent": "$http_user_agent", ' # user agent
  '"http_x_forwarded_for": "$http_x_forwarded_for", ' # http_x_forwarded_for
  '"http_host": "$http_host", ' # the request Host: header
  '"server_name": "$server_name", ' # the name of the vhost serving the request
  '"request_time": "$request_time", ' # request processing time in seconds with msec resolution
  '"upstream": "$upstream_addr", ' # upstream backend server for proxied requests
  '"upstream_connect_time": "$upstream_connect_time", ' # upstream handshake time incl. TLS
  '"upstream_header_time": "$upstream_header_time", ' # time spent receiving upstream headers
  '"upstream_response_time": "$upstream_response_time", ' # time spend receiving upstream body
  '"upstream_response_length": "$upstream_response_length", ' # upstream response length
  '"upstream_cache_status": "$upstream_cache_status", ' # cache HIT/MISS where applicable
  '"ssl_protocol": "$ssl_protocol", ' # TLS protocol
  '"ssl_cipher": "$ssl_cipher", ' # TLS cipher
  '"scheme": "$scheme", ' # http or https
  '"request_method": "$request_method", ' # request method
  '"server_protocol": "$server_protocol", ' # request protocol, like HTTP/1.1 or HTTP/2.0
  '"pipe": "$pipe", ' # "p" if request was pipelined, "." otherwise
  '"gzip_ratio": "$gzip_ratio", '
  '"http_cf_ray": "$http_cf_ray",'
  '"geoip_country_code": "$geoip2_data_country_code"'

server {

  access_log  /var/log/nginx/my-app-access.log;
  access_log  /var/log/nginx/my-app-json-access.log json_analytics;
  error_log   /var/log/nginx/my-app-error.log;


Restart nginx:

nginx -t
service nginx reload

You might want to use the nginx template instead of directly editing the application nginx file. View the dokku nginx configuration docs for more info.

Grafana Dashboards

Now finally to put it all together. We'll set up the following Grafana dashboards:

Click on each of the links above to view the corresponding json files for each dashboard. You can import these json files into Grafana by visiting and clicking on "Import".

Supporting Articles

Articles I referred to when setting this all up:


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