# Services

Configuring How to Reach the Services
{: .subtitle }

![services](../../assets/img/services.png)

The `Services` are responsible for configuring how to reach the actual services that will eventually handle the incoming requests. 

## Configuration Example

??? example "Declaring an HTTP Service with Two Servers -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [http.services]
      [http.services.my-service.loadBalancer]

        [[http.services.my-service.loadBalancer.servers]]
          url = "http://private-ip-server-1/"
        [[http.services.my-service.loadBalancer.servers]]
          url = "http://private-ip-server-2/"
    ```
    
    ```yaml tab="YAML"
    http:
      services:
        my-service:
          loadBalancer:
            servers:
            - url: "http://private-ip-server-1/"
            - url: "http://private-ip-server-2/"
    ```

??? example "Declaring a TCP Service with Two Servers -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [tcp.services]
      [tcp.services.my-service.loadBalancer]
         [[tcp.services.my-service.loadBalancer.servers]]
           address = "xx.xx.xx.xx:xx"
         [[tcp.services.my-service.loadBalancer.servers]]
           address = "xx.xx.xx.xx:xx"
    ```
    
    ```yaml tab="YAML"
    tcp:
      services:
        my-service:
          loadBalancer:         
            servers:
            - address: "xx.xx.xx.xx:xx"
            - address: "xx.xx.xx.xx:xx"
    ```

## Configuring HTTP Services

### Servers Load Balancer

The load balancers are able to load balance the requests between multiple instances of your programs. 

??? example "Declaring a Service with Two Servers (with Load Balancing) -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [http.services]
      [http.services.my-service.loadBalancer]

        [[http.services.my-service.loadBalancer.servers]]
          url = "http://private-ip-server-1/"
        [[http.services.my-service.loadBalancer.servers]]
          url = "http://private-ip-server-2/"
    ```

    ```yaml tab="YAML"
    http:
      services:
        my-service:
          loadBalancer:
            servers:
            - url: "http://private-ip-server-1/"
            - url: "http://private-ip-server-2/"
    ```

#### Servers

Servers declare a single instance of your program.
The `url` option point to a specific instance. 

!!! note
    Paths in the servers' `url` have no effet. 
    If you want the requests to be sent to a specific path on your servers,
    configure your [`routers`](../routers/index.md) to use a corresponding [middleware](../../middlewares/overview.md) (e.g. the [AddPrefix](../../middlewares/addprefix.md) or [ReplacePath](../../middlewares/replacepath.md)) middlewares.

??? example "A Service with One Server -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [http.services]
      [http.services.my-service.loadBalancer]
        [[http.services.my-service.loadBalancer.servers]]
          url = "http://private-ip-server-1/"
    ```
    
    ```yaml tab="YAML"
    http:
      services:
        my-service:
          loadBalancer:
            servers:
              - url: "http://private-ip-server-1/"
    ```

#### Load-balancing

For now, only round robin load balancing is supported:

??? example "Load Balancing -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [http.services]
      [http.services.my-service.loadBalancer]
        [[http.services.my-service.loadBalancer.servers]]
          url = "http://private-ip-server-1/"
        [[http.services.my-service.loadBalancer.servers]]
          url = "http://private-ip-server-2/"
    ```

    ```yaml tab="YAML"
    http:
      services:
        my-service:
          loadBalancer:
            servers:
            - url: "http://private-ip-server-1/"
            - url: "http://private-ip-server-2/"
    ```

#### Sticky sessions
  
When sticky sessions are enabled, a cookie is set on the initial request to track which server handles the first response.
On subsequent requests, the client is forwarded to the same server.

!!! note "Stickiness & Unhealthy Servers"
   
    If the server specified in the cookie becomes unhealthy, the request will be forwarded to a new server (and the cookie will keep track of the new server).

!!! note "Cookie Name" 
    
    The default cookie name is an abbreviation of a sha1 (ex: `_1d52e`).

!!! note "Secure & HTTPOnly flags"

    By default, the affinity cookie is created without those flags. One however can change that through configuration. 

??? example "Adding Stickiness"

    ```toml tab="TOML"
    [http.services]
      [http.services.my-service]
        [http.services.my-service.loadBalancer.sticky.cookie]
    ```
    
    ```yaml tab="YAML"
    http:
      services:
        my-service:
          loadBalancer:
            sticky:
             cookie: {}
    ```

??? example "Adding Stickiness with custom Options"

    ```toml tab="TOML"
    [http.services]
      [http.services.my-service]
        [http.services.my-service.loadBalancer.sticky.cookie]
          name = "my_sticky_cookie_name"
          secure = true
          httpOnly = true
    ```

    ```yaml tab="YAML"
    http:
      services:
        my-service:
          loadBalancer:
            sticky:
              cookie:
                name: my_sticky_cookie_name
                secure: true
                httpOnly: true
    ```

#### Health Check

Configure health check to remove unhealthy servers from the load balancing rotation.
Traefik will consider your servers healthy as long as they return status codes between `2XX` and `3XX` to the health check requests (carried out every `interval`).

Below are the available options for the health check mechanism:

- `path` is appended to the server URL to set the health check endpoint.
- `scheme`, if defined, will replace the server URL `scheme` for the health check endpoint
- `hostname`, if defined, will replace the server URL `hostname` for the health check endpoint.
- `port`, if defined, will replace the server URL `port` for the health check endpoint.
- `interval` defines the frequency of the health check calls.
- `timeout` defines the maximum duration Traefik will wait for a health check request before considering the server failed (unhealthy).
- `headers` defines custom headers to be sent to the health check endpoint.

!!! note "Interval & Timeout Format"

    Interval and timeout are to be given in a format understood by [time.ParseDuration](https://golang.org/pkg/time/#ParseDuration).
    The interval must be greater than the timeout. If configuration doesn't reflect this, the interval will be set to timeout + 1 second.

!!! note "Recovering Servers"
   
    Traefik keeps monitoring the health of unhealthy servers. 
    If a server has recovered (returning `2xx` -> `3xx` responses again), it will be added back to the load balacer rotation pool.

??? example "Custom Interval & Timeout -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [http.services]
      [http.servicess.Service-1]
        [http.services.Service-1.loadBalancer.healthCheck]
          path = "/health"
          interval = "10s"
          timeout = "3s"
    ```

    ```yaml tab="YAML"
    http:
      servicess:
        Service-1:
          loadBalancer:
            healthCheck:
              path: /health
              interval: "10s"
              timeout: "3s"
    ```

??? example "Custom Port -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [http.services]
      [http.services.Service-1]
        [http.services.Service-1.loadBalancer.healthCheck]
          path = "/health"
          port = 8080
    ```
    
    ```yaml tab="YAML"
    http:
      services:
        Service-1:
          loadBalancer:
            healthCheck:
              path: /health
              port: 8080
    ```

??? example "Custom Scheme -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [http.services]
      [http.services.Service-1]
        [http.services.Service-1.loadBalancer.healthCheck]
          path = "/health"
          scheme = "http"
    ```
    
    ```yaml tab="YAML"
    http:
      services:
        Service-1:
          loadBalancer:
            healthCheck:
              path: /health
              scheme: http
    ```

??? example "Additional HTTP Headers -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [http.services]
      [http.services.Service-1]
        [http.services.Service-1.loadBalancer.healthCheck]
          path = "/health"

          [http.services.Service-1.loadBalancer.healthCheck.headers]
            My-Custom-Header = "foo"
            My-Header = "bar"
    ```
    
    ```yaml tab="YAML"
    http:
      services:
        Service-1:
          loadBalancer:
            healthCheck:
              path: /health
              headers:
                My-Custom-Header: foo
                My-Header: bar
    ```

### Weighted Round Robin (service)

The WRR is able to load balance the requests between multiple services based on weights.

This strategy is only available to load balance between [services](./index.md) and not between [servers](./index.md#servers).

This strategy can be defined only with [File](../../providers/file.md).

```toml tab="TOML"
[http.services]
  [http.services.app]
    [[http.services.app.weighted.services]]
      name = "appv1"
      weight = 3
    [[http.services.app.weighted.services]]
      name = "appv2"
      weight = 1

  [http.services.appv1]
    [http.services.appv1.loadBalancer]
      [[http.services.appv1.loadBalancer.servers]]
        url = "http://private-ip-server-1/"

  [http.services.appv2]
    [http.services.appv2.loadBalancer]
      [[http.services.appv2.loadBalancer.servers]]
        url = "http://private-ip-server-2/"
```

```yaml tab="YAML"
http:
  services:
    app:
      weighted:
        services:
        - name: appv1
          weight: 3
        - name: appv2
          weight: 1

    appv1:
      loadBalancer:
        servers:
        - url: "http://private-ip-server-1/"

    appv2:
      loadBalancer:
        servers:
        - url: "http://private-ip-server-2/"
```

### Mirroring (service)

The mirroring is able to mirror requests sent to a service to other services.

This strategy can be defined only with [File](../../providers/file.md).

```toml tab="TOML"
[http.services]
  [http.services.mirrored-api]
    [http.services.mirrored-api.mirroring]
      service = "appv1"
    [[http.services.mirrored-api.mirroring.mirrors]]
      name = "appv2"
      percent = 10

  [http.services.appv1]
    [http.services.appv1.loadBalancer]
      [[http.services.appv1.loadBalancer.servers]]
        url = "http://private-ip-server-1/"

  [http.services.appv2]
    [http.services.appv2.loadBalancer]
      [[http.services.appv2.loadBalancer.servers]]
        url = "http://private-ip-server-2/"
```

```yaml tab="YAML"
http:
  services:
    mirrored-api:
      mirroring:
        service: appv1
        mirrors:
        - name: appv2
          percent: 10

    appv1:
      loadBalancer:
        servers:
        - url: "http://private-ip-server-1/"

    appv2:
      loadBalancer:
        servers:
        - url: "http://private-ip-server-2/"
```

## Configuring TCP Services

### General

Currently, `LoadBalancer` is the only supported kind of TCP `Service`.
However, since Traefik is an ever evolving project, other kind of TCP Services will be available in the future,
reason why you have to specify it. 

### Load Balancer

The load balancers are able to load balance the requests between multiple instances of your programs. 

??? example "Declaring a Service with Two Servers -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [tcp.services]
      [tcp.services.my-service.loadBalancer]
        [[tcp.services.my-service.loadBalancer.servers]]
          address = "xx.xx.xx.xx:xx"
        [[tcp.services.my-service.loadBalancer.servers]]
           address = "xx.xx.xx.xx:xx"
    ```

    ```yaml tab="YAML"
    tcp:
      services:
        my-service:
          loadBalancer:
            servers:
            - address: "xx.xx.xx.xx:xx"
            - address: "xx.xx.xx.xx:xx"
    ```

#### Servers

Servers declare a single instance of your program.
The `address` option (IP:Port) point to a specific instance.

??? example "A Service with One Server -- Using the [File Provider](../../providers/file.md)"

    ```toml tab="TOML"
    [tcp.services]
      [tcp.services.my-service.loadBalancer]
        [[tcp.services.my-service.loadBalancer.servers]]
          address = "xx.xx.xx.xx:xx"
    ```

    ```yaml tab="YAML"
    tcp:
      services:
        my-service:
          loadBalancer:
            servers:
              address: "xx.xx.xx.xx:xx"
    ```