Configure Prometheus to use non-default port

Question

I would like to install Prometheus on port 8080 instead of 9090 (its normal default). To this end I have edited /etc/systemd/system/prometheus.service to contain this line:

ExecStart=/usr/local/bin/prometheus \
  --config.file=/etc/prometheus.yaml --web.enable-admin-api \
  --web.listen-address=":8080"

I.e., I am using option --web.listen-address to specifiy the non-default port.

However, when I start Prometheus (2.0 beta) with systemctl start prometheus I receive this error message:

parse external URL "": invalid external URL "http://<myhost>:8080\"/"

So how can I configure Prometheus such that I can reach its web UI at http://<myhost>:8080/ (instead of http://<myhost>:9090)?

Merely

Answer 1

The quotes were superfluous. This line will work:

ExecStart=/usr/local/bin/prometheus \
  --config.file=/etc/prometheus.yaml --web.enable-admin-api \
  --web.listen-address=:8080

Merely

Answer 2

I'm using Ubuntu 20.02. It requires:

--web.listen-address=:8080  #defaults to  IPv6
--web.listen-address=*:8080 # does not work
--web.listen-address=192.168.1.X:8080 # for IPv4

Clowers

does config file really not have option for this? I can't believe it. – Asaph

look into /etc/default/prometheus @Asaph – Heavyladen

Answer 3

There is a default config location for prometheus & prometheus-node-exporter.

Both support --web.listen-address=host:port in their respective config files in /etc/default/prometheus and /etc/default/prometheus-node-exporter

It is noteworthy that prometheus & node-exporter will prefer to bind to an ipv6 (if ipv6 interface is present) using the default config value:

--web.listen-address=:9090

In that case, Prometheus will not bind to ipv4 interface and is only available with ipv6. Many people do not want this, and should set default listener interface explicitly.

These files in /etc/default/ are automatically read by the service units when starting up. It is not paradigmatic to modify the service unit, if there is a config file for the purpose.

Counterintuitively, it is not /etc/prometheus/prometheus.yml, because this file only describes prometheus workloads not the system service configuration.

Heavyladen