SSL Expiry and Uptime Monitor for URLs - Prometheus Blackbox | Grafana

In this article, we are going to see how to monitor your web services or URLs for their SSL expiry and uptime.

You can consider this as your SSL certificate expiry monitor and web service uptime monitor or URL Health check monitor for all your web services (URLs)

These are the set of tools we are going to need

  • Prometheus
  • Prometheus Blackbox ( exporter for URL monitoring )
  • alert manager ( for creating alerts )
  • Grafana ( for visualization )
  • Slack (for alerts and notifications )

We can go ahead and install all these tools on our chosen server. I am taking Centos7 but you can choose any Linux or windows as per your choice.

It is a lengthy article but do not be frightened. the result is going to be a milestone and solve some real problems.

this is what your end goal is going to look like. ( for some motivation )

Grafana URL and SSL monitor

And this is how your SSL certificate expiry alert is going to look like in SLACK

This is how your URL uptime monitor alert is going to look like

uptime slack alert prometheus

I can sense that you are already excited. Let's go ahead and get this setup done with no further ado.


Download links

  • Prometheus and Blackbox exporter, alert manager - Download here
  • Grafana - Download here

Prometheus Installation

once you have downloaded the binaries for your distribution, you just need to extract/untar to install.

I have used /opt/prometheus as my base directory to install Prometheus.

[[email protected] /opt/prometheus ]$ ls -lrt
total 161676
-rwxr-xr-x 1 3434 3434 87729971 Oct 15  2020 prometheus
-rwxr-xr-x 1 3434 3434 77801407 Oct 15  2020 promtool
-rw-r--r – 1 3434 3434      926 Oct 15  2020 prometheus.yml
drwxr-xr-x 2 3434 3434      173 Oct 15  2020 consoles
drwxr-xr-x 2 3434 3434       38 Oct 15  2020 console_libraries
-rw-r--r – 1 3434 3434     3420 Oct 15  2020 NOTICE
-rw-r--r – 1 3434 3434    11357 Oct 15  2020 LICENSE
drwxr-xr-x 4 root root       70 Nov  5  2020 data

you will see a list of files like shown above.

the primary configuration file is Prometheus.yml which we need to update later.

Alert Manager installation

Like Prometheus, an alert manager is also distributed as a tar.gz file. you can extract it into any directory

in my case it is /opt/alertmanager

[[email protected] /opt/alertmanager]# ls -lrt
total 47788
-rwxr-xr-x 1 3434 3434 27074026 Jun  2 07:51 alertmanager
-rwxr-xr-x 1 3434 3434 21839682 Jun  2 07:52 amtool
-rw-r--r – 1 3434 3434      457 Jun  2 07:56 NOTICE
-rw-r--r – 1 3434 3434    11357 Jun  2 07:56 LICENSE
-rw-r--r – 1 3434 3434      348 Jun  2 07:56 alertmanager.yml

you will see a set of files and alertmanager.yml is the primary configuration file which we will update later.


Blackbox Exporter Installation

Just like the other two previous installations, we need to extract the binaries of BlackBox into a directory

in my case it is /opt/blackbox

upon extracting you will see a list of files like this

[[email protected] /opt/blackbox]# ls -lrt
total 17812
-rwxr-xr-x 1 3434 3434 18217362 May 10 12:57 blackbox_exporter
-rw-r--r – 1 3434 3434       94 May 10 13:04 NOTICE
-rw-r--r – 1 3434 3434    11357 May 10 13:04 LICENSE
-rw-r--r – 1 3434 3434      672 May 10 13:04 blackbox.yml
[[email protected] blackbox]#

in this blackbox.yml is the primary configuration file

Change the ownership

After extracting/installing, you can see the ownership of these files is set to some numeric user.

You have to change the ownership of these installation directories to your desired user.

you can either create individual accounts for products like prometheus  , blackbox etc.

but I don't see any issues in running these products as a root  so am changing the ownership of all these directories and their contents to root

chown -R root:root /opt/prometheus
chown -R root:root /opt/blackbox
chown -R root:root /opt/alertmanager

Create Services for the tools

Now, as we have installed the three tools promethues, blackbox exporter, alert manager we can go ahead and start them.

the proper way to start these tools is with a service and it can be set up by creating a .service file under /etc/systemd/system

you have to create three files

touch prometheus.service
touch alertmanager.service
touch blackbox.service

once the files are created, you can open the files with vi or nano and update the contents

I have used root as a service user. if you have individual accounts created for these services you can update the User variable on the file before copying

Prometheus.service file


ExecStart=/opt/prometheus/prometheus – config.file=/opt/prometheus/prometheus.yml


alertmanager.service file


ExecStart=/opt/alertmanager/alertmanager – config.file=/opt/alertmanager/alertmanager.yml


BlackBox.service file


ExecStart=/opt/blackbox/blackbox_exporter – config.file=/opt/blackbox/blackbox.yml


Enable Services at boot

As you have created the service you can enable them to start at boot. as a startup script.

You can do this simply by enabling them using systemctl

systemctl enable prometheus.service
systemctl enable blackbox.service
systemctl enable alertmanager.service


Starting Prometheus, Alertmanager, blackbox

Now you can go ahead and start the service with the default configuration and validate if they can start properly.

sudo service prometheus start
sudo service alertmanager start
sudo service blackbox start

you can use ps -eaf or service status commands to validate if the services are running fine

Validate Prometheus UI

Now validate, if the Prometheus UI is up and running on port 9090

you can use curl

curl http://localhost:9090/graph

or you can reach from the external world if your security group and firewall allows it

for centos users, you need to additionally enable the port on firewall-cmd

# to add a new port to public zone
$ sudo firewall-cmd – zone=public – permanent – add-port=9090/tcp

# to reload the configuration for the changes to take effect
$ sudo firewall-cmd – reload

# to validate if the port is added
$ sudo firewall-cmd – list-all

the UI looks like this without any graphs

Prometheus UI

Configuring Prometheus

At this stage, we have installed all the necessary tools and validated the UI.

Now let's configure Prometheus to work with the alert manager and BlackBox exporter.

Prometheus is well known for its pull strategy and it pulls the metrics from various exporters and it has proven to be scalable and efficient in certain cases.

If you are having questions about why the pull approach is being used by Prometheus read this article

Our first objective is to make Prometheus pull metrics from blackbox exporter

Creating BlackBox job in Prometheus

Go to the installation directory of our Prometheus  in my case it is /opt/prometheus and edit the prometheus.yml file

under scrape_configs add a new job  named blackbox with the following snippet

- job_name: 'blackbox'
  metrics_path: /probe
   module: [http_2xx] # Look for a HTTP 200 response.
  - targets:
    - source_labels: [__address__]
      target_label: __param_target
    - source_labels: [__param_target]
      target_label: instance
    - target_label: __address__

you can change the URLs of your choice. but the relabel_configs should remain the same.

Validate the configuration before Applying - promtool

As we have made changes in prometheus.yml file.  It is always recommended to validate it before and restarting or reloading Prometheus

Prometheus comes with a tool named promtool which is available on the same directory where you have installed Prometheus

in my case it is /opt/prometheus

you can run the promtool check config command to validate the file.

[[email protected] ]$ /opt/prometheus/promtool check config /opt/prometheus/prometheus.yml
Checking /opt/prometheus/prometheus.yml
  SUCCESS: 0 rule files found

In case of no errors found. you will see SUCCESS a message like above.

Configuring Blackbox exporter

the default BlackBox is designed to support ipv6 which could create issues when we are using non ipv6 targets or system

So it is recommended to go with ipv4 for now.

In this step, we are going to update the default blackbox.yml configuration with ipv4 preference

we are going to add these two lines in the http probe

     preferred_ip_protocol: ip4

Here is the full configuration file for your reference. you can copy this and paste it to your blackbox.yml file.

    prober: http
     preferred_ip_protocol: ip4
    prober: http
      method: POST
    prober: tcp
    prober: tcp
      - expect: "^+OK"
      tls: true
        insecure_skip_verify: false
    prober: tcp
      - expect: "^SSH-2.0-"
      - send: "SSH-2.0-blackbox-ssh-check"
    prober: tcp
      - send: "NICK prober"
      - send: "USER prober prober prober :prober"
      - expect: "PING :([^ ]+)"
        send: "PONG ${1}"
      - expect: "^:[^ ]+ 001"


Restart Blackbox and Prometheus and Validate

Now it is time to restart our blackbox and prometheus as we have made changes to the configuration files of both.

sudo service prometheus restart
sudo service blackbox restart

Before we try to access the BlackBox and Prometheus UI interface.

we can validate if the ports are listening for both services.

# with ss command
[[email protected] blackbox]$ ss -tunlp|egrep '9115|9090'
tcp    LISTEN     0      128    [::]:9115               [::]:*                   users:(("blackbox_export",pid=4548,fd=3))
tcp    LISTEN     0      128    [::]:9090               [::]:*                   users:(("prometheus",pid=3302,fd=10))

# with netstat 
[[email protected] blackbox]$ netstat -tunlp|egrep '9115|9090'
tcp6       0      0 :::9115                 :::*                    LISTEN      4548/blackbox_expor
tcp6       0      0 :::9090                 :::*                    LISTEN      3302/prometheus

as you can see we are validating if the ports 9115 (blackbox_exporter) and 9090 (Prometheus) are listening.

blackbox exporter

For some reason, if the black box exporter not able to reach the target.  the result would be marked as Failure

you can use the corresponding Logs to investigate the Failure.

Now let us validate Prometheus and see if these targets are showing up, by going to http://server_name:9090/targets

prometheus blackbox

you can see our URLs in target and as an instance

the State will be marked as down in case of failure to reach the target.


Creating Graphs in Prometheus based on metrics of our URLs

In Prometheus UI, click on graph menu and choose any of the probes on the query block. for example probe_http_duration_seconds and click on Execute

you will see some graph given below.

Prometheus Graph

you can try different probes and try to create graphs of your interest.

Now we are successfully monitoring our web services (URLs)

Configuring Alerts and Rules in Prometheus

As part of Alert triggering, we are going to setup alerts for two scenarios

  • SSLCertExpiringSoon ( with in 4 days )
  • TargetUrlDown (Endpoint down or returning invalid response)

To generate alerts we need to create rules in Prometheus first.

If the rules are satisfied Prometheus would send the alert to AlertManager which can further be sent as email or slack notifications

Perform the following steps to create a new rule

Create a new Rule file

Go to Prometheus installation directory i.e /opt/prometheus and create a new directory named rules

under rules directory. create a new file named blackbox-rules.yml

copy the following content and paste it.

  - name: Blackbox rules
      - alert: SSLCertExpiringSoon
        expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 4
        for: 1m
          severity: warning
          description: "TLS certificate will expire in {{ $value | humanizeDuration }} (instance {{ $labels.instance }})"

      - alert: EndpointDown
        expr: probe_success == 0
        for: 10m
          severity: "critical"
          summary: "Endpoint {{ $labels.instance }} down"

As you can see in the preceding snippet, we are having two alerts defined SSLCertExpiry and EndPoint down.

both of these alerts takes black box probes as the source data

SSLCert Expiry alert is using probe_ssl_earliest_cert_expiry and Endpoint down uses probe_success

for the SSL Cert Expiry: If the earliest cert expiry value is below  86400 * 4   4 days it would trigger an alert.

If you want to increase the number of days. you can change 4 to the number of days of your choice.

Here, 86400 represents the seconds in a day 24 hours = 86400 seconds

Now let us map this rule into Prometheus configuration


Adding a rule into prometheus.yml

the rule file can now be added into our prometheus.yml configuration file

under the rule_files add our recently created rule filename rules/blackbox-rules.yml

   - "rules/blackbox-rules.yml"


Enabling the alert manager in prometheus.yml

While you are adding new rules. you have to also enable the alertmanager configuration which is disabled by default

It should point to the localhost:9093

# Alertmanager configuration
  - static_configs:
    - targets:
       - localhost:9093


The Final prometheus.yml file with alert manager and rules

# my global config
  scrape_interval:     120s # Set the scrape interval to every 15 seconds. Default is every 1 minute.
  evaluation_interval: 120s # Evaluate rules every 15 seconds. The default is every 1 minute.
  # scrape_timeout is set to the global default (10s).

# Alertmanager configuration
  - static_configs:
    - targets:
       - localhost:9093

# Load rules once and periodically evaluate them according to the global 'evaluation_interval'.
   - "rules/blackbox-rules.yml"

# A scrape configuration containing exactly one endpoint to scrape:
# Here it's Prometheus itself.
  # The job name is added as a label `job=<job_name>` to any timeseries scraped from this config.
  - job_name: 'prometheus'

    # metrics_path defaults to '/metrics'
    # scheme defaults to 'http'.

    - targets: ['localhost:9090']

  - job_name: 'blackbox'
    metrics_path: /probe
     module: [http_2xx] # Look for a HTTP 200 response.
    - targets:
      - source_labels: [__address__]
        target_label: __param_target
      - source_labels: [__param_target]
        target_label: instance
      - target_label: __address__


Validate the rule file and prometheus.yml with promtool

Now after making the changes, you can re-launch the promtool to validate

You should see SUCCESS and the number of rules displayed as shown below

[email protected] ]# /opt/prometheus/promtool check config /opt/prometheus/prometheus.yml
Checking /opt/prometheus/prometheus.yml
  SUCCESS: 1 rule files found

Checking /opt/prometheus/rules/blackbox-rules.yml
  SUCCESS: 2 rules found


Configuring Alertmanager - Adding Slack route

Now go to the alertmanager installation location and update the alertmanager.yml file with the following content.

Make sure you update the slack_api_url and the channel name according to your requirement.

 resolve_timeout: 1m

 receiver: 'slack-notifications'

- name: 'slack-notifications'
    - channel: '#devops'
      send_resolved: true
      title: |-
        [{{ .Status | toUpper }}{{ if eq .Status "firing" }}:{{ .Alerts.Firing | len }}{{ end }}] {{ .CommonLabels.alertname }} for {{ .CommonLabels.job }}
        {{- if gt (len .CommonLabels) (len .GroupLabels) -}}
          {{" "}}(
          {{- with .CommonLabels.Remove .GroupLabels.Names }}
            {{- range $index, $label := .SortedPairs -}}
              {{ if $index }}, {{ end }}
              {{- $label.Name }}="{{ $label.Value -}}"
            {{- end }}
          {{- end -}}
        {{- end }}
      text: >-
        @here Please check these alerts from Prometheus
        {{ range .Alerts -}}
        *Alert:* {{ .Annotations.title }}{{ if .Labels.severity }} - `{{ .Labels.severity }}`{{ end }}

        *Description:* {{ .Annotations.description }}

          {{ range .Labels.SortedPairs }} • *{{ .Name }}:* `{{ .Value }}`
          {{ end }}
        {{ end }}

to know how to create slack webhooks refer to this article


Now you can restart the alert manager service

validate if all the ports are open and the services are listening using ss

[[email protected] rules]# ss -tunlp|egrep '9115|9090|9093'
tcp    LISTEN     0      128    [::]:9115               [::]:*                   users:(("blackbox_export",pid=7841,fd=3))
tcp    LISTEN     0      128    [::]:9090               [::]:*                   users:(("prometheus",pid=8507,fd=9))
tcp    LISTEN     0      128    [::]:9093               [::]:*                   users:(("alertmanager",pid=13439,fd=8))


To Generate some Dummy alerts and to check if the alertmanager is working and slack notifications are triggering.

I have updated the blackbox-rules.yml file with 300 days instead of 4 days

- alert: SSLCertExpiringSoon
        expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 300

Validate the Rules in Prometheus UI

Go to http://serverip:9090/rules to validate the rules

rules prometheus

Validate the Alerts in Prometheus UI

Go to http://serverip:9090/alerts to see the alerts triggering

prometheus alerts

Validate your Slack Channel for notification

If you have done everything right, you should see a message in your configured slack channel.

as per my alertmanager.yml configuration it is devops channel

Slack Alert Prometheus

you can customize the message or the icons as per your need.

so we have met our objective of setting up a URL uptime and SSL expiry monitor.

There is one more missing piece which is visualizing our victory. with Grafana.


Installing Grafana

you can download Grafana from here and install on the same system where our other three products are running

Or simply you can type yum install grafana that would take care installing Grafana

start grafana-serverby issuing the following commands

sudo systemctl daemon-reload 
sudo systemctl start grafana-server 
sudo systemctl status grafana-server

the status command would show you the status the location of the configuration ini file

[[email protected] system]# systemctl status grafana-server
● grafana-server.service - Grafana instance
   Loaded: loaded (/usr/lib/systemd/system/grafana-server.service; enabled; vendor preset: disabled)
   Active: active (running) since Sat 2021-06-26 12:28:06 UTC; 2min 33s ago
 Main PID: 28798 (grafana-server)
   CGroup: /system.slice/grafana-server.service
           └─28798 /usr/sbin/grafana-server – config=/etc/grafana/grafana.ini – pidfile=/var/run/grafana/ – pa...

Jun 26 12:28:06 ip-172-45-68-92 grafana-server[28798]: t=2021-06-26T12:28:06+0000 lvl=info msg="Executing migration" logger...kind"
Jun 26 12:28:06 ip-172-45-68-92 grafana-server[28798]: t=2021-06-26T12:28:06+0000 lvl=info msg="Executing migration" logger...e v1"
Jun 26 12:28:06 ip-172-45-68-92 grafana-server[28798]: t=2021-06-26T12:28:06+0000 lvl=info msg="Executing migration" logger...n_id"
Jun 26 12:28:06 ip-172-45-68-92 grafana-server[28798]: t=2021-06-26T12:28:06+0000 lvl=info msg="migrations completed" logge...457ms


enable grafana-server as a service to start at boot by issuing the following command

sudo systemctl enable grafana-server

Now try to reach grafana UI and Login

  1. Open your web browser and go to http://localhost:3000/. The default HTTP port that Grafana listens to is 3000 unless you have configured a different port.
  2. On the login page, enter admin for username and password.
  3. Click Log in. If login is successful, then you will see a prompt to change the password.
  4. Click OK on the prompt, then change your password.

Once logged in let us create a new dashboard.

  1. Go to dashboards by clicking on the Dashboards option on the left navigation menu
  2. Click on Manage
  3. Click on Import
  4. Enter the number 7587 on the text box under import via and click on LoadGrafana Import
  5. Choose the default  prometheus as the data source. since both Grafana and Prometheus runs on the same system you don't have to add Prometheus data source explicitly.

Grafana URL and SSL monitor



Hope you were able to follow and install all the necessary tools such as prometheus alertmanager , blackbox and grafana and get your alerting and slack integration setup.

I am sure this would help you solve some major issues in your infrastructure.



Sarav AK

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