title: "mapping values are not allowed in this context" Alertmanager.yml
body: <p>I'm using Alertmanager 0.20 with Prometheus. The configuration at alertmanager.yml is ok, but if I try to add the proxy_url once I'm behind a proxy, and according with the documentation <a href="https://prometheus.io/docs/alerting/latest/configuration/" rel="nofollow noreferrer">configuration</a>, we need to set proxy_url under http_config.</p>
  <p>Using those two, Alertmanager starts to fail with the following error:</p>
  <pre><code>systemd[1]: Stopped Alert Manager.
  systemd[1]: Started Alert Manager.
  alertmanager[22866]: level=info ts=2020-12-30T17:37:20.679Z caller=main.go:216 msg=&quot;Starting Alertmanager&quot; version=&quot;(version=0.21.0, branch=HEAD, revision=4c6c03ebfe21009c546e4d1e9b92c371d67c021d)&quot;
  alertmanager[22866]: level=info ts=2020-12-30T17:37:20.679Z caller=main.go:217 build_context=&quot;(go=go1.14.4, user=root@dee35927357f, date=20200617-08:54:02)&quot;
  alertmanager[22866]: level=info ts=2020-12-30T17:37:20.680Z caller=cluster.go:161 component=cluster msg=&quot;setting advertise address explicitly&quot; addr=xxx.xxx.xxx.xxx port=9094
  alertmanager[22866]: level=info ts=2020-12-30T17:37:20.681Z caller=cluster.go:623 component=cluster msg=&quot;Waiting for gossip to settle...&quot; interval=2s
  alertmanager[22866]: level=info ts=2020-12-30T17:37:20.705Z caller=coordinator.go:119 component=configuration msg=&quot;Loading configuration file&quot; file=/etc/prometheus/alertmanager.yml
  alertmanager[22866]: level=error ts=2020-12-30T17:37:20.705Z caller=coordinator.go:124 component=configuration msg=&quot;Loading configuration file failed&quot; file=/etc/prometheus/alertmanager.yml err=&quot;yaml: **line 4: mapping values are not allowed in this context**&quot;
  alertmanager[22866]: level=info ts=2020-12-30T17:37:20.705Z caller=cluster.go:632 component=cluster msg=&quot;gossip not settled but continuing anyway&quot; polls=0 elapsed=23.966326ms
  systemd[1]: alertmanager.service: Main process exited, code=exited, status=1/FAILURE
  systemd[1]: alertmanager.service: Failed with result 'exit-code'.
  prometheus[14952]: level=error ts=2020-12-30T17:37:20.779Z caller=notifier.go:527 component=notifier alertmanager=http://localhost:9093/api/v1/alerts count=2 msg=&quot;Error sending alert&quot; err=&quot;Post \&quot;http://localhost:9093/api/v1/alerts\&quot;: dial tcp [::1]:9093: connect: connection refused&quot;
  systemd[1]: alertmanager.service: Service RestartSec=100ms expired, scheduling restart.
  systemd[1]: alertmanager.service: Scheduled restart job, restart counter is at 5.
  systemd[1]: Stopped Alert Manager.
  systemd[1]: alertmanager.service: Start request repeated too quickly.
  systemd[1]: alertmanager.service: Failed with result 'exit-code'.
  systemd[1]: Failed to start Alert Manager.
  </code></pre>
  <p>My alertmanager version:</p>
  <pre><code>alertmanager, version 0.21.0 (branch: HEAD, revision:
  4c6c03ebfe21009c546e4d1e9b92c371d67c021d)   build user:      
  root@dee35927357f   build date:       20200617-08:54:02   go version: 
  go1.14.4
  </code></pre>
  <p>My alertmanager.yml</p>
  <pre><code>global:
  http_config:
  proxy_url: http://ip:port
   smtp_smarthost: smtp_server_name:port
   smtp_from: from@email.com
   smtp_auth_username: auth@email.com
  route:
    group_by: [alertname]
    repeat_interval: 1m
    receiver: live-monitoring
  
  receivers:
  - name: live-monitoring
    email_configs:
    - to: to@email.com
  </code></pre>
  <p>Any idea how to make alertmanager working and sending emails with the proxy configuration? And I can't set http_config and proxy_url before route: or receivers, otherwise</p>
  <pre><code>field http_config not found in type config.plain
  </code></pre>