# Prometheus monitoring

Prometheus is an open-source systems monitoring and alerting toolkit released in 2012. Prometheus design is focused to collect and process metrics, not as an event logging system for logs.

## Install Prometheus

* Linux: How To Install Prometheus in Linux
* macOS:
** brew install prometheus && brew services start prometheus
** brew install node_exporter. Connect to: http://localhost:9101/metrics
* Using Docker containers:
** docker pull prom/prometheus && docker run -p 9090:9090 prom/prometheus and connect to http://localhost:9090/
** docker pull prom/node-exporter although it's not recommended to deploy it as a Docker container because it requires access to the host system

## Configuration files

* Linux: /etc/prometheus/prometheus.yml
* macOS: /usr/local/etc/prometheus.args

## Binaries

* prometheus
* promtool

## Configuring Prometheus

* In the /etc/prometheus directory, use nano or your favorite text editor to create a configuration file named prometheus.yml. For now, this file will contain just enough information to run Prometheus for the first time.
    sudo nano /etc/prometheus/prometheus.yml
* In the global settings, define the default interval for scraping metrics. Note that Prometheus will apply these settings to every exporter unless an individual exporter's own settings override the global.
* This scrape_interval value tells Prometheus to collect metrics from its exporters every 15 seconds, which is long enough for most exporters. Now, add Prometheus itself to the list of exporters to scrape from with the following scrape_configs directive:
* Prometheus uses the job_name to label exporters in queries and on graphs, so be sure to pick something descriptive here. And, as Prometheus exports important data about itself that you can use for monitoring performance and debugging, we've overridden the global scrape_interval directive from 15 seconds to 5 seconds for more frequent updates. Lastly, Prometheus uses the static_configs and targets directives to determine where exporters are running. Since this particular exporter is running on the same server as Prometheus itself, we can use localhost instead of an IP address along with the default port, 9090.
Your configuration file should now look like this:

## Basic Prometheus Operations

* Start Prometheus: :sudo systemctl start prometheus
* Reload systemd: :sudo systemctl daemon-reload prometheus
* Verify the service's status: :sudo systemctl status prometheus

## Installing Node Exporter
### Installing Node Exporter from Docker Hub

* docker pull prom/node-exporter && docker run prom/node-exporter

### Installing Node Exporter from Prometheus binary relases

To expand Prometheus beyond metrics about itself only, we'll install an additional exporter called Node Exporter. Node Exporter provides detailed information about the system, including CPU, disk, and memory usage.
* Download the current stable version of Node Exporter into your home directory.
* Use the sha256sum command to generate a checksum of the downloaded file: sha256sum node_exporter-0.15.1.linux-amd64.tar.gz
* Unpack the downloaded archive: tar xvf node_exporter-0.15.1.linux-amd64.tar.gz
* This will create a directory called node_exporter-0.15.1.linux-amd64 containing a binary file named node_exporter, a license, and a notice.
* Copy the binary to the /usr/local/bin directory and set the user and group ownership to the node_exporter user that you created in Step 1 and remove the leftover files from your home directory as they are no longer needed.
Now that you've installed Node Exporter, let's test it out by running it before creating a service file for it so that it starts on boot.

## Running Node Exporter

The steps for running Node Exporter are similar to those for running Prometheus itself. Start by creating the Systemd service file for Node Exporter and copy the following content into the service file:
* Reload systemd to use the newly created service: :sudo systemctl daemon-reload
* Run Node Exporter using the following command: :sudo systemctl start node_exporter
* Verify that Node Exporter's running correctly: :sudo systemctl status node_exporter
* Lastly, enable Node Exporter to start on boot.

### Configuring Prometheus to Scrape Node Exporter

Because Prometheus only scrapes exporters which are defined in the scrape_configs portion of its configuration file, we'll need to add an entry for Node Exporter, just like we did for Prometheus itself.
At the end of the scrape_configs block, add a new entry called node_exporter.
Finally, restart Prometheus to put the changes into effect and verify status

## Activities

* Install Prometheus in Linux, Run Prometheus in Linux and connect to graphical interface http://localhost:9090/graph
* Read Prometheus changelog: https://github.com/prometheus/prometheus/blob/master/CHANGELOG.md
* Read Stackoverflow prometheus questions: https://stackoverflow.com/questions/tagged/prometheus?tab=Frequent