traefik/docs/toml.md

# Global configuration

## Main section

```toml
# traefik.toml
################################################################
# Global configuration
################################################################

# Traefik logs file
# If not defined, logs to stdout
#
# Optional
#
# traefikLogsFile = "log/traefik.log"

# Access logs file
#
# Optional
#
# accessLogsFile = "log/access.log"

# Log level
#
# Optional
# Default: "ERROR"
#
# logLevel = "ERROR"

# Backends throttle duration: minimum duration between 2 events from providers
# before applying a new configuration. It avoids unnecessary reloads if multiples events
# are sent in a short amount of time.
#
# Optional
# Default: "2s"
#
# ProvidersThrottleDuration = "5s"

# If non-zero, controls the maximum idle (keep-alive) to keep per-host.  If zero, DefaultMaxIdleConnsPerHost is used.
# If you encounter 'too many open files' errors, you can either change this value, or change `ulimit` value.
#
# Optional
# Default: http.DefaultMaxIdleConnsPerHost
#
# MaxIdleConnsPerHost = 200

# Entrypoints to be used by frontends that do not specify any entrypoint.
# Each frontend can specify its own entrypoints.
#
# Optional
# Default: ["http"]
#
# defaultEntryPoints = ["http", "https"]
```

## Entrypoints definition

```toml
# Entrypoints definition
#
# Optional
# Default:
# [entryPoints]
#   [entryPoints.http]
#   address = ":80"
#
# To redirect an http entrypoint to an https entrypoint (with SNI support):
# [entryPoints]
#   [entryPoints.http]
#   address = ":80"
#     [entryPoints.http.redirect]
#       entryPoint = "https"
#   [entryPoints.https]
#   address = ":443"
#     [entryPoints.https.tls]
#       [[entryPoints.https.tls.certificates]]
#       CertFile = "integration/fixtures/https/snitest.com.cert"
#       KeyFile = "integration/fixtures/https/snitest.com.key"
#       [[entryPoints.https.tls.certificates]]
#       CertFile = "integration/fixtures/https/snitest.org.cert"
#       KeyFile = "integration/fixtures/https/snitest.org.key"
#
# To redirect an entrypoint rewriting the URL:
# [entryPoints]
#   [entryPoints.http]
#   address = ":80"
#     [entryPoints.http.redirect]
#       regex = "^http://localhost/(.*)"
#       replacement = "http://mydomain/$1"

[entryPoints]
  [entryPoints.http]
  address = ":80"
```

## Retry configuration

```toml
# Enable retry sending request if network error
#
# Optional
#
[retry]

# Number of attempts
#
# Optional
# Default: (number servers in backend) -1
#
# attempts = 3
```

## ACME (Let's Encrypt) configuration

```toml
# Sample entrypoint configuration when using ACME
[entryPoints]
  [entryPoints.https]
  address = ":443"
    [entryPoints.https.tls]

# Enable ACME (Let's Encrypt): automatic SSL
#
# Optional
#
[acme]

# Email address used for registration
#
# Required
#
email = "test@traefik.io"

# File used for certificates storage.
# WARNING, if you use Traefik in Docker, you have 2 options:
#  - create a file on your host and mount it has a volume
#      storageFile = "acme.json"
#      $ docker run -v "/my/host/acme.json:acme.json" traefik
#  - mount the folder containing the file has a volume
#      storageFile = "/etc/traefik/acme/acme.json"
#      $ docker run -v "/my/host/acme:/etc/traefik/acme" traefik
#
# Required
#
storageFile = "acme.json"

# Entrypoint to proxy acme challenge to.
# WARNING, must point to an entrypoint on port 443
#
# Required
#
entryPoint = "https"

# Enable on demand certificate. This will request a certificate from Let's Encrypt during the first TLS handshake for a hostname that does not yet have a certificate.
# WARNING, TLS handshakes will be slow when requesting a hostname certificate for the first time, this can leads to DoS attacks.
# WARNING, Take note that Let's Encrypt have rate limiting: https://community.letsencrypt.org/t/quick-start-guide/1631
#
# Optional
#
# onDemand = true

# CA server to use
# Uncomment the line to run on the staging let's encrypt server
# Leave comment to go to prod
#
# Optional
#
# caServer = "https://acme-staging.api.letsencrypt.org/directory"

# Domains list
# You can provide SANs (alternative domains) to each main domain
# All domains must have A/AAAA records pointing to Traefik
# WARNING, Take note that Let's Encrypt have rate limiting: https://community.letsencrypt.org/t/quick-start-guide/1631
# Each domain & SANs will lead to a certificate request.
#
# [[acme.domains]]
#   main = "local1.com"
#   sans = ["test1.local1.com", "test2.local1.com"]
# [[acme.domains]]
#   main = "local2.com"
#   sans = ["test1.local2.com", "test2x.local2.com"]
# [[acme.domains]]
#   main = "local3.com"
# [[acme.domains]]
#   main = "local4.com"
[[acme.domains]]
   main = "local1.com"
   sans = ["test1.local1.com", "test2.local1.com"]
[[acme.domains]]
   main = "local3.com"
[[acme.domains]]
   main = "local4.com"
```

# Configuration backends

## File backend

Like any other reverse proxy, Træfɪk can be configured with a file. You have two choices:

- simply add your configuration at the end of the global configuration file `traefik.toml` :

```toml
# traefik.toml
logLevel = "DEBUG"
defaultEntryPoints = ["http", "https"]
[entryPoints]
  [entryPoints.http]
  address = ":80"
    [entryPoints.http.redirect]
      entryPoint = "https"
  [entryPoints.https]
  address = ":443"
    [entryPoints.https.tls]
      [[entryPoints.https.tls.certificates]]
      CertFile = "integration/fixtures/https/snitest.com.cert"
      KeyFile = "integration/fixtures/https/snitest.com.key"
      [[entryPoints.https.tls.certificates]]
      CertFile = "integration/fixtures/https/snitest.org.cert"
      KeyFile = "integration/fixtures/https/snitest.org.key"

[file]

# rules
[backends]
  [backends.backend1]
    [backends.backend1.circuitbreaker]
      expression = "NetworkErrorRatio() > 0.5"
    [backends.backend1.servers.server1]
    url = "http://172.17.0.2:80"
    weight = 10
    [backends.backend1.servers.server2]
    url = "http://172.17.0.3:80"
    weight = 1
  [backends.backend2]
    [backends.backend1.maxconn]
      amount = 10
      extractorfunc = "request.host"
    [backends.backend2.LoadBalancer]
      method = "drr"
    [backends.backend2.servers.server1]
    url = "http://172.17.0.4:80"
    weight = 1
    [backends.backend2.servers.server2]
    url = "http://172.17.0.5:80"
    weight = 2

[frontends]
  [frontends.frontend1]
  backend = "backend2"
    [frontends.frontend1.routes.test_1]
    rule = "Host:test.localhost"
  [frontends.frontend2]
  backend = "backend1"
  passHostHeader = true
  priority = 10
  entrypoints = ["https"] # overrides defaultEntryPoints
    [frontends.frontend2.routes.test_1]
    rule = "Host:{subdomain:[a-z]+}.localhost"
  [frontends.frontend3]
  entrypoints = ["http", "https"] # overrides defaultEntryPoints
  backend = "backend2"
    rule = "Path:/test"
```

- or put your rules in a separate file, for example `rules.toml`:

```toml
# traefik.toml
logLevel = "DEBUG"
[entryPoints]
  [entryPoints.http]
  address = ":80"
    [entryPoints.http.redirect]
      entryPoint = "https"
  [entryPoints.https]
  address = ":443"
    [entryPoints.https.tls]
      [[entryPoints.https.tls.certificates]]
      CertFile = "integration/fixtures/https/snitest.com.cert"
      KeyFile = "integration/fixtures/https/snitest.com.key"
      [[entryPoints.https.tls.certificates]]
      CertFile = "integration/fixtures/https/snitest.org.cert"
      KeyFile = "integration/fixtures/https/snitest.org.key"

[file]
filename = "rules.toml"
```

```toml
# rules.toml
[backends]
  [backends.backend1]
    [backends.backend1.circuitbreaker]
      expression = "NetworkErrorRatio() > 0.5"
    [backends.backend1.servers.server1]
    url = "http://172.17.0.2:80"
    weight = 10
    [backends.backend1.servers.server2]
    url = "http://172.17.0.3:80"
    weight = 1
  [backends.backend2]
    [backends.backend1.maxconn]
      amount = 10
      extractorfunc = "request.host"
    [backends.backend2.LoadBalancer]
      method = "drr"
    [backends.backend2.servers.server1]
    url = "http://172.17.0.4:80"
    weight = 1
    [backends.backend2.servers.server2]
    url = "http://172.17.0.5:80"
    weight = 2

[frontends]
  [frontends.frontend1]
  backend = "backend2"
    [frontends.frontend1.routes.test_1]
    rule = "Host:test.localhost"
  [frontends.frontend2]
  backend = "backend1"
  passHostHeader = true
  priority = 10
  entrypoints = ["https"] # overrides defaultEntryPoints
    [frontends.frontend2.routes.test_1]
    rule = "Host:{subdomain:[a-z]+}.localhost"
  [frontends.frontend3]
  entrypoints = ["http", "https"] # overrides defaultEntryPoints
  backend = "backend2"
    rule = "Path:/test"
```

If you want Træfɪk to watch file changes automatically, just add:

```toml
[file]
watch = true
```

## API backend

Træfik can be configured using a restful api.
To enable it:

```toml
[web]
address = ":8080"

# SSL certificate and key used
#
# Optional
#
# CertFile = "traefik.crt"
# KeyFile = "traefik.key"
#
# Set REST API to read-only mode
#
# Optional
# ReadOnly = false
```

- `/`: provides a simple HTML frontend of Træfik

![Web UI Providers](img/web.frontend.png)
![Web UI Health](img/traefik-health.png)

- `/health`: `GET` json metrics

```sh
$ curl -s "http://localhost:8080/health" | jq .
{
  // Træfɪk PID
  "pid": 2458,
  // Træfɪk server uptime (formated time)
  "uptime": "39m6.885931127s",
  //  Træfɪk server uptime in seconds
  "uptime_sec": 2346.885931127,
  // current server date
  "time": "2015-10-07 18:32:24.362238909 +0200 CEST",
  // current server date in seconds
  "unixtime": 1444235544,
  // count HTTP response status code in realtime
  "status_code_count": {
    "502": 1
  },
  // count HTTP response status code since Træfɪk started
  "total_status_code_count": {
    "200": 7,
    "404": 21,
    "502": 13
  },
  // count HTTP response
  "count": 1,
  // count HTTP response
  "total_count": 41,
  // sum of all response time (formated time)
  "total_response_time": "35.456865605s",
  // sum of all response time in seconds
  "total_response_time_sec": 35.456865605,
  // average response time (formated time)
  "average_response_time": "864.8016ms",
  // average response time in seconds
  "average_response_time_sec": 0.8648016000000001
}
```

- `/api`: `GET` configuration for all providers

```sh
$ curl -s "http://localhost:8080/api" | jq .
{
  "file": {
    "frontends": {
      "frontend2": {
        "routes": {
          "test_2": {
            "rule": "Path:/test"
          }
        },
        "backend": "backend1"
      },
      "frontend1": {
        "routes": {
          "test_1": {
            "rule": "Host:test.localhost"
          }
        },
        "backend": "backend2"
      }
    },
    "backends": {
      "backend2": {
        "loadBalancer": {
          "method": "drr"
        },
        "servers": {
          "server2": {
            "weight": 2,
            "URL": "http://172.17.0.5:80"
          },
          "server1": {
            "weight": 1,
            "url": "http://172.17.0.4:80"
          }
        }
      },
      "backend1": {
        "loadBalancer": {
          "method": "wrr"
        },
        "circuitBreaker": {
          "expression": "NetworkErrorRatio() > 0.5"
        },
        "servers": {
          "server2": {
            "weight": 1,
            "url": "http://172.17.0.3:80"
          },
          "server1": {
            "weight": 10,
            "url": "http://172.17.0.2:80"
          }
        }
      }
    }
  }
}
```

- `/api/providers`: `GET` providers
- `/api/providers/{provider}`: `GET` or `PUT` provider
- `/api/providers/{provider}/backends`: `GET` backends
- `/api/providers/{provider}/backends/{backend}`: `GET` a backend
- `/api/providers/{provider}/backends/{backend}/servers`: `GET` servers in a backend
- `/api/providers/{provider}/backends/{backend}/servers/{server}`: `GET` a server in a backend
- `/api/providers/{provider}/frontends`: `GET` frontends
- `/api/providers/{provider}/frontends/{frontend}`: `GET` a frontend
- `/api/providers/{provider}/frontends/{frontend}/routes`: `GET` routes in a frontend
- `/api/providers/{provider}/frontends/{frontend}/routes/{route}`: `GET` a route in a frontend


## Docker backend

Træfɪk can be configured to use Docker as a backend configuration:

```toml
################################################################
# Docker configuration backend
################################################################

# Enable Docker configuration backend
#
# Optional
#
[docker]

# Docker server endpoint. Can be a tcp or a unix socket endpoint.
#
# Required
#
endpoint = "unix:///var/run/docker.sock"

# Default domain used.
# Can be overridden by setting the "traefik.domain" label on a container.
#
# Required
#
domain = "docker.localhost"

# Enable watch docker changes
#
# Optional
#
watch = true

# Override default configuration template. For advanced users :)
#
# Optional
#
# filename = "docker.tmpl"

# Expose containers by default in traefik
#
# Optional
# Default: true
#
exposedbydefault = true

# Enable docker TLS connection
#
#  [docker.tls]
#  ca = "/etc/ssl/ca.crt"
#  cert = "/etc/ssl/docker.crt"
#  key = "/etc/ssl/docker.key"
#  insecureskipverify = true
```

Labels can be used on containers to override default behaviour:

- `traefik.backend=foo`: assign the container to `foo` backend
- `traefik.port=80`: register this port. Useful when the container exposes multiples ports.
- `traefik.protocol=https`: override the default `http` protocol
- `traefik.weight=10`: assign this weight to the container
- `traefik.enable=false`: disable this container in Træfɪk
- `traefik.frontend.rule=Host:test.traefik.io`: override the default frontend rule (Default: `Host:{containerName}.{domain}`).
- `traefik.frontend.passHostHeader=true`: forward client `Host` header to the backend.
- `traefik.frontend.priority=10`: override default frontend priority
- `traefik.frontend.entryPoints=http,https`: assign this frontend to entry points `http` and `https`. Overrides `defaultEntryPoints`.
- `traefik.docker.network`: Set the docker network to use for connections to this container


## Marathon backend

Træfɪk can be configured to use Marathon as a backend configuration:


```toml
################################################################
# Mesos/Marathon configuration backend
################################################################

# Enable Marathon configuration backend
#
# Optional
#
[marathon]

# Marathon server endpoint.
# You can also specify multiple endpoint for Marathon:
# endpoint := "http://10.241.1.71:8080,10.241.1.72:8080,10.241.1.73:8080"
#
# Required
#
endpoint = "http://127.0.0.1:8080"

# Enable watch Marathon changes
#
# Optional
#
watch = true

# Default domain used.
#
# Required
#
domain = "marathon.localhost"

# Override default configuration template. For advanced users :)
#
# Optional
#
# filename = "marathon.tmpl"

# Expose Marathon apps by default in traefik
#
# Optional
# Default: false
#
# exposedByDefault = true

# Convert Marathon groups to subdomains
# Default behavior: /foo/bar/myapp => foo-bar-myapp.{defaultDomain}
# with groupsAsSubDomains enabled: /foo/bar/myapp => myapp.bar.foo.{defaultDomain}
#
# Optional
# Default: false
#
# groupsAsSubDomains = true

# Enable Marathon basic authentication
#
# Optional
#
#  [marathon.basic]
#  httpBasicAuthUser = "foo"
#  httpBasicPassword = "bar"

# TLS client configuration. https://golang.org/pkg/crypto/tls/#Config
#
# Optional
#
# [marathon.TLS]
# InsecureSkipVerify = true

# DCOSToken for DCOS environment, This will override the Authorization header
#
# Optional
#
# dcosToken = "xxxxxx"
```

Labels can be used on containers to override default behaviour:

- `traefik.backend=foo`: assign the application to `foo` backend
- `traefik.portIndex=1`: register port by index in the application's ports array. Useful when the application exposes multiple ports.
- `traefik.port=80`: register the explicit application port value. Cannot be used alongside `traefik.portIndex`.
- `traefik.protocol=https`: override the default `http` protocol
- `traefik.weight=10`: assign this weight to the application
- `traefik.enable=false`: disable this application in Træfɪk
- `traefik.frontend.rule=Host:test.traefik.io`: override the default frontend rule (Default: `Host:{containerName}.{domain}`).
- `traefik.frontend.passHostHeader=true`: forward client `Host` header to the backend.
- `traefik.frontend.priority=10`: override default frontend priority
- `traefik.frontend.entryPoints=http,https`: assign this frontend to entry points `http` and `https`. Overrides `defaultEntryPoints`.


## Kubernetes Ingress backend


Træfɪk can be configured to use Kubernetes Ingress as a backend configuration:

```toml
################################################################
# Kubernetes Ingress configuration backend
################################################################
# Enable Kubernetes Ingress configuration backend
#
# Optional
#
[kubernetes]

# Kubernetes server endpoint
#
# When deployed as a replication controller in Kubernetes,
# Traefik will use env variable KUBERNETES_SERVICE_HOST
# and KUBERNETES_SERVICE_PORT_HTTPS as endpoint
# Secure token will be found in /var/run/secrets/kubernetes.io/serviceaccount/token
# and SSL CA cert in /var/run/secrets/kubernetes.io/serviceaccount/ca.crt
#
# Optional
#
# endpoint = "http://localhost:8080"
# namespaces = ["default","production"]
#
# See: http://kubernetes.io/docs/user-guide/labels/#list-and-watch-filtering
# labelselector = "A and not B"
#
```

Annotations can be used on containers to override default behaviour for the whole Ingress resource:

- `traefik.frontend.rule.type: PathPrefixStrip`: override the default frontend rule type (Default: `PathPrefix`).

You can find here an example [ingress](https://raw.githubusercontent.com/containous/traefik/master/examples/k8s.ingress.yaml) and [replication controller](https://raw.githubusercontent.com/containous/traefik/master/examples/k8s.rc.yaml).

## Consul backend

Træfɪk can be configured to use Consul as a backend configuration:

```toml
################################################################
# Consul KV configuration backend
################################################################

# Enable Consul KV configuration backend
#
# Optional
#
[consul]

# Consul server endpoint
#
# Required
#
endpoint = "127.0.0.1:8500"

# Enable watch Consul changes
#
# Optional
#
watch = true

# Prefix used for KV store.
#
# Optional
#
prefix = "traefik"

# Override default configuration template. For advanced users :)
#
# Optional
#
# filename = "consul.tmpl"

# Enable consul TLS connection
#
# Optional
#
# [consul.tls]
# ca = "/etc/ssl/ca.crt"
# cert = "/etc/ssl/consul.crt"
# key = "/etc/ssl/consul.key"
# insecureskipverify = true
```

Please refer to the [Key Value storage structure](#key-value-storage-structure) section to get documentation en traefik KV structure.

## Consul catalog backend

Træfɪk can be configured to use service discovery catalog of Consul as a backend configuration:

```toml
################################################################
# Consul Catalog configuration backend
################################################################

# Enable Consul Catalog configuration backend
#
# Optional
#
[consulCatalog]

# Consul server endpoint
#
# Required
#
endpoint = "127.0.0.1:8500"

# Default domain used.
#
# Optional
#
domain = "consul.localhost"

# Prefix for Consul catalog tags
#
# Optional
#
prefix = "traefik"
```

This backend will create routes matching on hostname based on the service name
used in consul.

Additional settings can be defined using Consul Catalog tags:

- `traefik.enable=false`: disable this container in Træfɪk
- `traefik.protocol=https`: override the default `http` protocol
- `traefik.backend.weight=10`: assign this weight to the container
- `traefik.backend.circuitbreaker=NetworkErrorRatio() > 0.5`
- `traefik.backend.loadbalancer=drr`: override the default load balancing mode
- `traefik.frontend.rule=Host:test.traefik.io`: override the default frontend rule (Default: `Host:{containerName}.{domain}`).
- `traefik.frontend.passHostHeader=true`: forward client `Host` header to the backend.
- `traefik.frontend.priority=10`: override default frontend priority
- `traefik.frontend.entryPoints=http,https`: assign this frontend to entry points `http` and `https`. Overrides `defaultEntryPoints`.

## Etcd backend

Træfɪk can be configured to use Etcd as a backend configuration:

```toml
################################################################
# Etcd configuration backend
################################################################

# Enable Etcd configuration backend
#
# Optional
#
[etcd]

# Etcd server endpoint
#
# Required
#
endpoint = "127.0.0.1:4001"

# Enable watch Etcd changes
#
# Optional
#
watch = true

# Prefix used for KV store.
#
# Optional
#
prefix = "/traefik"

# Override default configuration template. For advanced users :)
#
# Optional
#
# filename = "etcd.tmpl"

# Enable etcd TLS connection
#
# Optional
#
# [etcd.tls]
# ca = "/etc/ssl/ca.crt"
# cert = "/etc/ssl/etcd.crt"
# key = "/etc/ssl/etcd.key"
# insecureskipverify = true
```

Please refer to the [Key Value storage structure](#key-value-storage-structure) section to get documentation en traefik KV structure.


## Zookeeper backend

Træfɪk can be configured to use Zookeeper as a backend configuration:

```toml
################################################################
# Zookeeper configuration backend
################################################################

# Enable Zookeeperconfiguration backend
#
# Optional
#
[zookeeper]

# Zookeeper server endpoint
#
# Required
#
endpoint = "127.0.0.1:2181"

# Enable watch Zookeeper changes
#
# Optional
#
watch = true

# Prefix used for KV store.
#
# Optional
#
prefix = "/traefik"

# Override default configuration template. For advanced users :)
#
# Optional
#
# filename = "zookeeper.tmpl"
```

Please refer to the [Key Value storage structure](#key-value-storage-structure) section to get documentation en traefik KV structure.

## BoltDB backend

Træfɪk can be configured to use BoltDB as a backend configuration:

```toml
################################################################
# BoltDB configuration backend
################################################################

# Enable BoltDB configuration backend
#
# Optional
#
[boltdb]

# BoltDB file
#
# Required
#
endpoint = "/my.db"

# Enable watch BoltDB changes
#
# Optional
#
watch = true

# Prefix used for KV store.
#
# Optional
#
prefix = "/traefik"

# Override default configuration template. For advanced users :)
#
# Optional
#
# filename = "boltdb.tmpl"
```

Please refer to the [Key Value storage structure](#key-value-storage-structure) section to get documentation en traefik KV structure.

## Key-value storage structure

The Keys-Values structure should look (using `prefix = "/traefik"`):

- backend 1

| Key                                                    | Value                       |
|--------------------------------------------------------|-----------------------------|
| `/traefik/backends/backend1/circuitbreaker/expression` | `NetworkErrorRatio() > 0.5` |
| `/traefik/backends/backend1/servers/server1/url`       | `http://172.17.0.2:80`      |
| `/traefik/backends/backend1/servers/server1/weight`    | `10`                        |
| `/traefik/backends/backend1/servers/server2/url`       | `http://172.17.0.3:80`      |
| `/traefik/backends/backend1/servers/server2/weight`    | `1`                         |

- backend 2

| Key                                                 | Value                  |
|-----------------------------------------------------|------------------------|
| `/traefik/backends/backend2/maxconn/amount`         | `10`                   |
| `/traefik/backends/backend2/maxconn/extractorfunc`  | `request.host`         |
| `/traefik/backends/backend2/loadbalancer/method`    | `drr`                  |
| `/traefik/backends/backend2/servers/server1/url`    | `http://172.17.0.4:80` |
| `/traefik/backends/backend2/servers/server1/weight` | `1`                    |
| `/traefik/backends/backend2/servers/server2/url`    | `http://172.17.0.5:80` |
| `/traefik/backends/backend2/servers/server2/weight` | `2`                    |

- frontend 1

| Key                                               | Value                 |
|---------------------------------------------------|-----------------------|
| `/traefik/frontends/frontend1/backend`            | `backend2`            |
| `/traefik/frontends/frontend1/routes/test_1/rule` | `Host:test.localhost` |

- frontend 2

| Key                                                | Value              |
|----------------------------------------------------|--------------------|
| `/traefik/frontends/frontend2/backend`             | `backend1`         |
| `/traefik/frontends/frontend2/passHostHeader`      | `true`             |
| `/traefik/frontends/frontend2/priority`            | `10`               |
| `/traefik/frontends/frontend2/entrypoints`         | `http,https`       |
| `/traefik/frontends/frontend2/routes/test_2/rule`  | `PathPrefix:/test` |

## Atomic configuration changes

The [Etcd](https://github.com/coreos/etcd/issues/860) and [Consul](https://github.com/hashicorp/consul/issues/886) backends do not support updating multiple keys atomically. As a result, it may be possible for Træfɪk to read an intermediate configuration state despite judicious use of the `--providersThrottleDuration` flag. To solve this problem, Træfɪk supports a special key called `/traefik/alias`. If set, Træfɪk use the value as an alternative key prefix.

Given the key structure below, Træfɪk will use the `http://172.17.0.2:80` as its only backend (frontend keys have been omitted for brevity).

| Key                                                                     | Value                       |
|-------------------------------------------------------------------------|-----------------------------|
| `/traefik/alias`                                                        | `/traefik_configurations/1` |
| `/traefik_configurations/1/backends/backend1/servers/server1/url`       | `http://172.17.0.2:80`      |
| `/traefik_configurations/1/backends/backend1/servers/server1/weight`    | `10`                        |

When an atomic configuration change is required, you may write a new configuration at an alternative prefix. Here, although the `/traefik_configurations/2/...` keys have been set, the old configuration is still active because the `/traefik/alias` key still points to `/traefik_configurations/1`:

| Key                                                                     | Value                       |
|-------------------------------------------------------------------------|-----------------------------|
| `/traefik/alias`                                                        | `/traefik_configurations/1` |
| `/traefik_configurations/1/backends/backend1/servers/server1/url`       | `http://172.17.0.2:80`      |
| `/traefik_configurations/1/backends/backend1/servers/server1/weight`    | `10`                        |
| `/traefik_configurations/2/backends/backend1/servers/server1/url`       | `http://172.17.0.2:80`      |
| `/traefik_configurations/2/backends/backend1/servers/server1/weight`    | `5`                        |
| `/traefik_configurations/2/backends/backend1/servers/server2/url`       | `http://172.17.0.3:80`      |
| `/traefik_configurations/2/backends/backend1/servers/server2/weight`    | `5`                        |

Once the `/traefik/alias` key is updated, the new `/traefik_configurations/2` configuration becomes active atomically. Here, we have a 50% balance between the `http://172.17.0.3:80` and the `http://172.17.0.4:80` hosts while no traffic is sent to the `172.17.0.2:80` host:

| Key                                                                     | Value                       |
|-------------------------------------------------------------------------|-----------------------------|
| `/traefik/alias`                                                        | `/traefik_configurations/2` |
| `/traefik_configurations/1/backends/backend1/servers/server1/url`       | `http://172.17.0.2:80`      |
| `/traefik_configurations/1/backends/backend1/servers/server1/weight`    | `10`                        |
| `/traefik_configurations/2/backends/backend1/servers/server1/url`       | `http://172.17.0.3:80`      |
| `/traefik_configurations/2/backends/backend1/servers/server1/weight`    | `5`                        |
| `/traefik_configurations/2/backends/backend1/servers/server2/url`       | `http://172.17.0.4:80`      |
| `/traefik_configurations/2/backends/backend1/servers/server2/weight`    | `5`                        |

Note that Træfɪk *will not watch for key changes in the `/traefik_configurations` prefix*. It will only watch for changes in the `/traefik` prefix. Further, if the `/traefik/alias` key is set, all other sibling keys with the `/traefik` prefix are ignored.