gatus/README.md

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A service health dashboard in Go that is meant to be used as a docker 
image with a custom configuration file.

I personally deploy it in my Kubernetes cluster and let it monitor the status of my
core applications: https://status.twinnation.org/


## Table of Contents

- [Features](#features)
- [Usage](#usage)
  - [Configuration](#configuration)
  - [Conditions](#conditions)
    - [Placeholders](#placeholders)
    - [Functions](#functions)
  - [Alerting](#alerting)
    - [Configuring Slack alerts](#configuring-slack-alerts)
    - [Configuring PagerDuty alerts](#configuring-pagerduty-alerts)
    - [Configuring Twilio alerts](#configuring-twilio-alerts)
    - [Configuring custom alerts](#configuring-custom-alerts)
- [Docker](#docker)
- [Running the tests](#running-the-tests)
- [Using in Production](#using-in-production)
- [FAQ](#faq)
  - [Sending a GraphQL request](#sending-a-graphql-request)
  - [Recommended interval](#recommended-interval)
  - [Default timeouts](#default-timeouts)
  - [Monitoring a TCP service](#monitoring-a-tcp-service)


## Features

The main features of Gatus are:
- **Highly flexible health check conditions**: While checking the response status may be enough for some use cases, Gatus goes much further and allows you to add conditions on the response time, the response body and even the IP address.
- **Ability to use Gatus for user acceptance tests**: Thanks to the point above, you can leverage this application to create automated user acceptance tests.
- **Very easy to configure**: Not only is the configuration designed to be as readable as possible, it's also extremely easy to add a new service or a new endpoint to monitor.
- **Alerting**: While having a pretty visual dashboard is useful to keep track of the state of your application(s), you probably don't want to stare at it all day. Thus, notifications via Slack, PagerDuty and Twilio are supported out of the box with the ability to configure a custom alerting provider for any needs you might have, whether it be a different provider or a custom application that manages automated rollbacks. 
- **Metrics**
- **Low resource consumption**: As with most Go applications, the resource footprint that this application requires is negligibly small.


## Usage

By default, the configuration file is expected to be at `config/config.yaml`.

You can specify a custom path by setting the `GATUS_CONFIG_FILE` environment variable.

Here's a simple example:

```yaml
metrics: true         # Whether to expose metrics at /metrics
services:
  - name: twinnation  # Name of your service, can be anything
    url: "https://twinnation.org/health"
    interval: 30s     # Duration to wait between every status check (default: 60s)
    conditions:
      - "[STATUS] == 200"         # Status must be 200
      - "[BODY].status == UP"     # The json path "$.status" must be equal to UP
      - "[RESPONSE_TIME] < 300"   # Response time must be under 300ms
  - name: example
    url: "https://example.org/"
    interval: 30s
    conditions:
      - "[STATUS] == 200"
```

This example would look like this:

![Simple example](.github/assets/example.png)

Note that you can also add environment variables in the configuration file (i.e. `$DOMAIN`, `${DOMAIN}`)


### Configuration

| Parameter                                | Description                                                                   | Default        |
|:---------------------------------------- |:----------------------------------------------------------------------------- |:-------------- |
| `debug`                                  | Whether to enable debug logs                                                  | `false`        |
| `metrics`                                | Whether to expose metrics at /metrics                                         | `false`        |
| `services`                               | List of services to monitor                                                   | Required `[]`  |
| `services[].name`                        | Name of the service. Can be anything.                                         | Required `""`  |
| `services[].url`                         | URL to send the request to                                                    | Required `""`  |
| `services[].conditions`                  | Conditions used to determine the health of the service                        | `[]`           |
| `services[].insecure`                    | Whether to skip verifying the server's certificate chain and host name        | `false`        |
| `services[].interval`                    | Duration to wait between every status check                                   | `60s`          |
| `services[].method`                      | Request method                                                                | `GET`          |
| `services[].graphql`                     | Whether to wrap the body in a query param (`{"query":"$body"}`)               | `false`        |
| `services[].body`                        | Request body                                                                  | `""`           |
| `services[].headers`                     | Request headers                                                               | `{}`           |
| `services[].alerts[].type`               | Type of alert. Valid types: `slack`, `pagerduty`, `twilio`, `custom`          | Required `""`  |
| `services[].alerts[].enabled`            | Whether to enable the alert                                                   | `false`        |
| `services[].alerts[].failure-threshold`  | Number of failures in a row needed before triggering the alert                | `3`            |
| `services[].alerts[].success-threshold`  | Number of successes in a row before an ongoing incident is marked as resolved | `2`            |
| `services[].alerts[].send-on-resolved`   | Whether to send a notification once a triggered alert is marked as resolved   | `false`        |
| `services[].alerts[].description`        | Description of the alert. Will be included in the alert sent                  | `""`           |
| `alerting`                               | Configuration for alerting                                                    | `{}`           |
| `alerting.slack`                         | Configuration for alerts of type `slack`                                      | `{}`           |
| `alerting.slack.webhook-url`             | Slack Webhook URL                                                             | Required `""`  |
| `alerting.pagerduty`                     | Configuration for alerts of type `pagerduty`                                  | `{}`           |
| `alerting.pagerduty.integration-key`     | PagerDuty Events API v2 integration key.                                      | Required `""`  |
| `alerting.twilio`                        | Settings for alerts of type `twilio`                                          | `{}`           |
| `alerting.twilio.sid`                    | Twilio account SID                                                            | Required `""`  |
| `alerting.twilio.token`                  | Twilio auth token                                                             | Required `""`  |
| `alerting.twilio.from`                   | Number to send Twilio alerts from                                             | Required `""`  |
| `alerting.twilio.to`                     | Number to send twilio alerts to                                               | Required `""`  |
| `alerting.custom`                        | Configuration for custom actions on failure or alerts                         | `{}`           |
| `alerting.custom.url`                    | Custom alerting request url                                                   | Required `""`  |
| `alerting.custom.body`                   | Custom alerting request body.                                                 | `""`           |
| `alerting.custom.headers`                | Custom alerting request headers                                               | `{}`           |
| `security`                               | Security configuration                                                        | `{}`           |
| `security.basic`                         | Basic authentication security configuration                                   | `{}`           |
| `security.basic.username`                | Username for Basic authentication                                             | Required `""`  |
| `security.basic.password-sha512`         | Password's SHA512 hash for Basic authentication                               | Required `""`  |


### Conditions

Here are some examples of conditions you can use:

| Condition                    | Description                                             | Passing values             | Failing values |
|:-----------------------------|:------------------------------------------------------- |:-------------------------- | -------------- |
| `[STATUS] == 200`            | Status must be equal to 200                             | 200                        | 201, 404, ...  |
| `[STATUS] < 300`             | Status must lower than 300                              | 200, 201, 299              | 301, 302, ...  |
| `[STATUS] <= 299`            | Status must be less than or equal to 299                | 200, 201, 299              | 301, 302, ...  |
| `[STATUS] > 400`             | Status must be greater than 400                         | 401, 402, 403, 404         | 400, 200, ...  |
| `[CONNECTED] == true`        | Connection to host must've been successful              | true, false                |  |
| `[RESPONSE_TIME] < 500`      | Response time must be below 500ms                       | 100ms, 200ms, 300ms        | 500ms, 501ms   |
| `[IP] == 127.0.0.1`          | Target IP must be 127.0.0.1                             | 127.0.0.1                  | 0.0.0.0        |
| `[BODY] == 1`                | The body must be equal to 1                             | 1                          | `{}`, `2`, ... |
| `[BODY].user.name == john`   | JSONPath value of `$.user.name` is equal to `john`      | `{"user":{"name":"john"}}` |  |
| `[BODY].data[0].id == 1`     | JSONPath value of `$.data[0].id` is equal to 1          | `{"data":[{"id":1}]}`      |  |
| `[BODY].age == [BODY].id`    | JSONPath value of `$.age` is equal JSONPath `$.id`      | `{"age":1,"id":1}`         |  |
| `len([BODY].data) < 5`       | Array at JSONPath `$.data` has less than 5 elements     | `{"data":[{"id":1}]}`      |  |
| `len([BODY].name) == 8`      | String at JSONPath `$.name` has a length of 8           | `{"name":"john.doe"}`      | `{"name":"bob"}` |
| `[BODY].name == pat(john*)`  | String at JSONPath `$.name` matches pattern `john*`     | `{"name":"john.doe"}`      | `{"name":"bob"}` |


#### Placeholders

| Placeholder             | Description                                             | Example of resolved value |
|:----------------------- |:------------------------------------------------------- |:------------------------- |
| `[STATUS]`              | Resolves into the HTTP status of the request            | 404
| `[RESPONSE_TIME]`       | Resolves into the response time the request took, in ms | 10
| `[IP]`                  | Resolves into the IP of the target host                 | 192.168.0.232
| `[BODY]`                | Resolves into the response body. Supports JSONPath.     | `{"name":"john.doe"}`
| `[CONNECTED]`           | Resolves into whether a connection could be established | `true`


#### Functions

| Function   | Description                                                                                                      | Example                    |
|:-----------|:---------------------------------------------------------------------------------------------------------------- |:-------------------------- |
| `len`      | Returns the length of the object/slice. Works only with the `[BODY]` placeholder.                                | `len([BODY].username) > 8`
| `pat`      | Specifies that the string passed as parameter should be evaluated as a pattern. Works only with `==` and `!=`.   | `[IP] == pat(192.168.*)`

**NOTE**: Use `pat` only when you need to. `[STATUS] == pat(2*)` is a lot more expensive than `[STATUS] < 300`.



### Alerting


#### Configuring Slack alerts

```yaml
alerting:
  slack: 
    webhook-url: "https://hooks.slack.com/services/**********/**********/**********"
services:
  - name: twinnation
    url: "https://twinnation.org/health"
    interval: 30s
    alerts:
      - type: slack
        enabled: true
        description: "healthcheck failed 3 times in a row"
        send-on-resolved: true
      - type: slack
        enabled: true
        failure-threshold: 5
        description: "healthcheck failed 5 times in a row"
        send-on-resolved: true
    conditions:
      - "[STATUS] == 200"
      - "[BODY].status == UP"
      - "[RESPONSE_TIME] < 300"
```

Here's an example of what the notifications look like:

![Slack notifications](.github/assets/slack-alerts.png)


#### Configuring PagerDuty alerts

It is highly recommended to set `services[].alerts[].send-on-resolved` to `true` for alerts 
of type `pagerduty`, because unlike other alerts, the operation resulting from setting said 
parameter to `true` will not create another incident, but mark the incident as resolved on 
PagerDuty instead. 

```yaml
alerting:
  pagerduty: 
    integration-key: "********************************"
services:
  - name: twinnation
    url: "https://twinnation.org/health"
    interval: 30s
    alerts:
      - type: pagerduty
        enabled: true
        failure-threshold: 3
        success-threshold: 5
        send-on-resolved: true
        description: "healthcheck failed 3 times in a row"
    conditions:
      - "[STATUS] == 200"
      - "[BODY].status == UP"
      - "[RESPONSE_TIME] < 300"
```


#### Configuring Twilio alerts

```yaml
alerting:
  twilio:
    sid: "..."
    token: "..."
    from: "+1-234-567-8901"
    to: "+1-234-567-8901"
services:
  - name: twinnation
    interval: 30s
    url: "https://twinnation.org/health"
    alerts:
      - type: twilio
        enabled: true
        failure-threshold: 5
        send-on-resolved: true
        description: "healthcheck failed 5 times in a row"
    conditions:
      - "[STATUS] == 200"
      - "[BODY].status == UP"
      - "[RESPONSE_TIME] < 300"
```


#### Configuring custom alerts

While they're called alerts, you can use this feature to call anything. 

For instance, you could automate rollbacks by having an application that keeps tracks of new deployments, and by 
leveraging Gatus, you could have Gatus call that application endpoint when a service starts failing. Your application
would then check if the service that started failing was recently deployed, and if it was, then automatically 
roll it back.

The values `[ALERT_DESCRIPTION]` and `[SERVICE_NAME]` are automatically substituted for the alert description and the 
service name respectively in the body (`alerting.custom.body`) as well as the url (`alerting.custom.url`).

If you have `send-on-resolved` set to `true`, you may want to use `[ALERT_TRIGGERED_OR_RESOLVED]` to differentiate
the notifications. It will be replaced for either `TRIGGERED` or `RESOLVED`, based on the situation.

For all intents and purpose, we'll configure the custom alert with a Slack webhook, but you can call anything you want.

```yaml
alerting:
  custom:
    url: "https://hooks.slack.com/services/**********/**********/**********"
    method: "POST"
    body: |
      {
        "text": "[ALERT_TRIGGERED_OR_RESOLVED]: [SERVICE_NAME] - [ALERT_DESCRIPTION]"
      }
services:
  - name: twinnation
    url: "https://twinnation.org/health"
    interval: 30s
    alerts:
      - type: custom
        enabled: true
        failure-threshold: 10
        success-threshold: 3
        send-on-resolved: true
        description: "healthcheck failed 10 times in a row"
    conditions:
      - "[STATUS] == 200"
      - "[BODY].status == UP"
      - "[RESPONSE_TIME] < 300"
```


## Docker

Other than using one of the examples provided in the `examples` folder, you can also try it out locally by 
creating a configuration file - we'll call it `config.yaml` for this example - and running the following 
command:
```
docker run -p 8080:8080 --mount type=bind,source="$(pwd)"/config.yaml,target=/config/config.yaml --name gatus twinproduction/gatus
```

If you're on Windows, replace `"$(pwd)"` by the absolute path to your current directory, e.g.:
```
docker run -p 8080:8080 --mount type=bind,source=C:/Users/Chris/Desktop/config.yaml,target=/config/config.yaml --name gatus twinproduction/gatus
```

## Running the tests

```
go test ./... -mod vendor
```


## Using in Production

See the [example](example) folder.


## FAQ

### Sending a GraphQL request

By setting `services[].graphql` to true, the body will automatically be wrapped by the standard GraphQL `query` parameter.

For instance, the following configuration:
```yaml
services:
  - name: filter users by gender
    url: http://localhost:8080/playground
    method: POST
    graphql: true
    body: |
      {
        user(gender: "female") {
          id
          name
          gender
          avatar
        }
      }
    headers:
      Content-Type: application/json
    conditions:
      - "[STATUS] == 200"
      - "[BODY].data.user[0].gender == female"
```

will send a `POST` request to `http://localhost:8080/playground` with the following body:
```json
{"query":"      {\n        user(gender: \"female\") {\n          id\n          name\n          gender\n          avatar\n        }\n      }"}
```


### Recommended interval

To ensure that Gatus provides reliable and accurate results (i.e. response time), Gatus only evaluates one service at a time. 
In other words, even if you have multiple services with the exact same interval, they will not execute at the same time.

You can test this yourself by running Gatus with several services configured with a very short, unrealistic interval, 
such as 1ms. You'll notice that the response time does not fluctuate - that is because while services are evaluated on
different goroutines, there's a global lock that prevents multiple services from running at the same time.

Unfortunately, there is a drawback. If you have a lot of services, including some that are very slow or prone to time out (the default
time out is 10s for HTTP and 5s for TCP), then it means that for the entire duration of the request, no other services can be evaluated.

**This does mean that Gatus will be unable to evaluate the health of other services**. 
The interval does not include the duration of the request itself, which means that if a service has an interval of 30s 
and the request takes 2s to complete, the timestamp between two evaluations will be 32s, not 30s. 

While this does not prevent Gatus' from performing health checks on all other services, it may cause Gatus to be unable 
to respect the configured interval, for instance:
- Service A has an interval of 5s, and times out after 10s to complete 
- Service B has an interval of 5s, and takes 1ms to complete
- Service B will be unable to run every 5s, because service A's health evaluation takes longer than its interval

To sum it up, while Gatus can really handle any interval you throw at it, you're better off having slow requests with 
higher interval.

As a rule of the thumb, I personally set interval for more complex health checks to `5m` (5 minutes) and 
simple health checks used for alerting (PagerDuty/Twilio) to `30s`.


### Default timeouts

| Protocol | Timeout |
|:-------- |:------- |
| HTTP     | 10s
| TCP      | 5s


### Monitoring a TCP service

By prefixing `services[].url` with `tcp:\\`, you can monitor TCP services at a very basic level:

```yaml
  - name: redis
    url: "tcp://127.0.0.1:6379"
    interval: 30s
    conditions:
      - "[CONNECTED] == true"
```

Placeholders `[STATUS]` and `[BODY]` as well as the fields `services[].body`, `services[].insecure`, 
`services[].headers`, `services[].method` and `services[].graphql` are not supported for TCP services.

**NOTE**: `[CONNECTED] == true` does not guarantee that the service itself is healthy - it only guarantees that there's 
something at the given address listening to the given port, and that a connection to that address was successfully 
established.


### Basic authentication

You can require Basic authentication by leveraging the `security.basic` configuration:

```yaml
security:
  basic:
    username: "john.doe"
    password-sha512: "6b97ed68d14eb3f1aa959ce5d49c7dc612e1eb1dafd73b1e705847483fd6a6c809f2ceb4e8df6ff9984c6298ff0285cace6614bf8daa9f0070101b6c89899e22"
```

The example above will require that you authenticate with the username `john.doe` as well as the password `hunter2`.