prometheus: prometheus 2.2.1 marathon_sd_config doesn't work properly

What did you do? I have setup for sd_marathon_config in prometheus.yml

What did you see instead? Under which circumstances?

I saw below error:

level=error ts=2018-04-10T14:07:21.991899244Z caller=marathon.go:187 component="discovery manager scrape" discovery=marathon msg="Error while updating services" err="invalid character '<' looking for beginning of value"

Environment Prometheus version: 2.2.1 Alert Manager: 0.14.0

• Alertmanager version:

0.14.0

• Prometheus version:

2.2.1

• Prometheus configuration file:

- job_name: marathon
  scrape_interval: 15s
  scrape_timeout: 10s
  metrics_path: /metrics
  scheme: http
  marathon_sd_configs:
  - servers:
    - http://marathon.url
    timeout: 30s
    refresh_interval: 30s
  relabel_configs:
  - source_labels: [__meta_marathon_app]
    separator: ;
    regex: ^/(.+)
    target_label: app
    replacement: $1
    action: replace
  - source_labels: [app]
    separator: ;
    regex: (service-a|service-b)
    replacement: $1
    action: keep
  - source_labels: [app]
    separator: ;
    regex: (service-a|service-b)
    target_label: __metrics_path__
    replacement: /prometheus
    action: replace```