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Basics

Concepts

Let's take our example from the overview again:

Imagine that you have deployed a bunch of microservices on your infrastructure. You probably used a service registry (like etcd or consul) and/or an orchestrator (swarm, Mesos/Marathon) to manage all these services. If you want your users to access some of your microservices from the Internet, you will have to use a reverse proxy and configure it using virtual hosts or prefix paths:

• domain api.domain.com will point the microservice api in your private network
• path domain.com/web will point the microservice web in your private network
• domain backoffice.domain.com will point the microservices backoffice in your private network, load-balancing between your multiple instances

Let's zoom on Traefik and have an overview of its internal architecture:

• Incoming requests end on entrypoints, as the name suggests, they are the network entry points into Traefik (listening port, SSL, traffic redirection...).
• Traffic is then forwarded to a matching frontend. A frontend defines routes from entrypoints to backends. Routes are created using requests fields (Host, Path, Headers...) and can match or not a request.
• The frontend will then send the request to a backend. A backend can be composed by one or more servers, and by a load-balancing strategy.
• Finally, the server will forward the request to the corresponding microservice in the private network.

Entrypoints

Entrypoints are the network entry points into Traefik. They can be defined using:

• a port (80, 443...)
• SSL (Certificates, Keys, authentication with a client certificate signed by a trusted CA...)
• redirection to another entrypoint (redirect HTTP to HTTPS)

Here is an example of entrypoints definition:

[entryPoints]
  [entryPoints.http]
  address = ":80"
    [entryPoints.http.redirect]
    entryPoint = "https"
  [entryPoints.https]
  address = ":443"
    [entryPoints.https.tls]
      [[entryPoints.https.tls.certificates]]
      certFile = "tests/traefik.crt"
      keyFile = "tests/traefik.key"

• Two entrypoints are defined http and https.
• http listens on port 80 and https on port 443.
• We enable SSL on https by giving a certificate and a key.
• We also redirect all the traffic from entrypoint http to https.

And here is another example with client certificate authentication:

[entryPoints]
  [entryPoints.https]
  address = ":443"
  [entryPoints.https.tls]
    [entryPoints.https.tls.ClientCA]
    files = ["tests/clientca1.crt", "tests/clientca2.crt"]
    optional = false
    [[entryPoints.https.tls.certificates]]
    certFile = "tests/traefik.crt"
    keyFile = "tests/traefik.key"

• We enable SSL on https by giving a certificate and a key.
• One or several files containing Certificate Authorities in PEM format are added.
• It is possible to have multiple CA's in the same file or keep them in separate files.

Frontends

A frontend consists of a set of rules that determine how incoming requests are forwarded from an entrypoint to a backend.

Rules may be classified in one of two groups: Modifiers and matchers.

Modifiers

Modifier rules only modify the request. They do not have any impact on routing decisions being made.

Following is the list of existing modifier rules:

• AddPrefix: /products: Add path prefix to the existing request path prior to forwarding the request to the backend.
• ReplacePath: /serverless-path: Replaces the path and adds the old path to the X-Replaced-Path header. Useful for mapping to AWS Lambda or Google Cloud Functions.
• ReplacePathRegex: ^/api/v2/(.*) /api/$1: Replaces the path with a regular expression and adds the old path to the X-Replaced-Path header. Separate the regular expression and the replacement by a space.

Matchers

Matcher rules determine if a particular request should be forwarded to a backend.

The associativity rule is the following:

• , is the OR operator (works only inside a matcher, ex: Host:foo.com,bar.com).
  • i.e., forward a request if any rule matches.
  • Does not work for Headers and HeadersRegexp.
• ; is the AND operator (works only between matchers, ex: Host:foo.com;Path:/bar)
  • i.e., forward a request if all rules match

Following is the list of existing matcher rules along with examples:

Matcher	Description
Headers: Content-Type, application/json	Match HTTP header. It accepts a comma-separated key/value pair where both key and value must be literals.
HeadersRegexp: Content-Type, application/(text/json)	Match HTTP header. It accepts a comma-separated key/value pair where the key must be a literal and the value may be a literal or a regular expression.
Host: traefik.io, www.traefik.io	Match request host. It accepts a sequence of literal hosts.
HostRegexp: traefik.io, {subdomain:[a-z]+}.traefik.io	Match request host. It accepts a sequence of literal and regular expression hosts.
Method: GET, POST, PUT	Match request HTTP method. It accepts a sequence of HTTP methods.
Path: /products/, /articles/{category}/{id:[0-9]+}	Match exact request path. It accepts a sequence of literal and regular expression paths.
PathStrip: /products/	Match exact path and strip off the path prior to forwarding the request to the backend. It accepts a sequence of literal paths.
PathStripRegex: /articles/{category}/{id:[0-9]+}	Match exact path and strip off the path prior to forwarding the request to the backend. It accepts a sequence of literal and regular expression paths.
PathPrefix: /products/, /articles/{category}/{id:[0-9]+}	Match request prefix path. It accepts a sequence of literal and regular expression prefix paths.
PathPrefixStrip: /products/	Match request prefix path and strip off the path prefix prior to forwarding the request to the backend. It accepts a sequence of literal prefix paths. Starting with Traefik 1.3, the stripped prefix path will be available in the X-Forwarded-Prefix header.
PathPrefixStripRegex: /articles/{category}/{id:[0-9]+}	Match request prefix path and strip off the path prefix prior to forwarding the request to the backend. It accepts a sequence of literal and regular expression prefix paths. Starting with Traefik 1.3, the stripped prefix path will be available in the X-Forwarded-Prefix header.
Query: foo=bar, bar=baz	Match Query String parameters. It accepts a sequence of key=value pairs.

In order to use regular expressions with Host and Path matchers, you must declare an arbitrarily named variable followed by the colon-separated regular expression, all enclosed in curly braces. Any pattern supported by Go's regexp package may be used (example: /posts/{id:[0-9]+}).

Note

The variable has no special meaning; however, it is required by the gorilla/mux dependency which embeds the regular expression and defines the syntax.

You can optionally enable passHostHeader to forward client Host header to the backend. You can also optionally configure the passTLSClientCert option to pass the Client certificates to the backend in a specific header.

Path Matcher Usage Guidelines

This section explains when to use the various path matchers.

Use Path if your backend listens on the exact path only. For instance, Path: /products would match /products but not /products/shoes.

Use a *Prefix* matcher if your backend listens on a particular base path but also serves requests on sub-paths. For instance, PathPrefix: /products would match /products but also /products/shoes and /products/shirts. Since the path is forwarded as-is, your backend is expected to listen on /products.

Use a *Strip matcher if your backend listens on the root path (/) but should be routeable on a specific prefix. For instance, PathPrefixStrip: /products would match /products but also /products/shoes and /products/shirts.
Since the path is stripped prior to forwarding, your backend is expected to listen on /.
If your backend is serving assets (e.g., images or Javascript files), chances are it must return properly constructed relative URLs.
Continuing on the example, the backend should return /products/shoes/image.png (and not /images.png which Traefik would likely not be able to associate with the same backend).
The X-Forwarded-Prefix header (available since Traefik 1.3) can be queried to build such URLs dynamically.

Instead of distinguishing your backends by path only, you can add a Host matcher to the mix. That way, namespacing of your backends happens on the basis of hosts in addition to paths.

Examples

Here is an example of frontends definition:

[frontends]
  [frontends.frontend1]
  backend = "backend2"
    [frontends.frontend1.routes.test_1]
    rule = "Host:test.localhost,test2.localhost"
  [frontends.frontend2]
  backend = "backend1"
  passHostHeader = true
  [frontends.frontend2.passTLSClientCert]
    pem = true
  priority = 10
  entrypoints = ["https"] # overrides defaultEntryPoints
    [frontends.frontend2.routes.test_1]
    rule = "HostRegexp:localhost,{subdomain:[a-z]+}.localhost"
  [frontends.frontend3]
  backend = "backend2"
    [frontends.frontend3.routes.test_1]
    rule = "Host:test3.localhost;Path:/test"

• Three frontends are defined: frontend1, frontend2 and frontend3
• frontend1 will forward the traffic to the backend2 if the rule Host:test.localhost,test2.localhost is matched
• frontend2 will forward the traffic to the backend1 if the rule HostRegexp:localhost,{subdomain:[a-z]+}.localhost is matched (forwarding client Host header to the backend)
• frontend3 will forward the traffic to the backend2 if the rules Host:test3.localhost AND Path:/test are matched

Combining multiple rules

As seen in the previous example, you can combine multiple rules. In TOML file, you can use multiple routes:

  [frontends.frontend3]
  backend = "backend2"
    [frontends.frontend3.routes.test_1]
    rule = "Host:test3.localhost"
    [frontends.frontend3.routes.test_2]
    rule = "Path:/test"

Here frontend3 will forward the traffic to the backend2 if the rules Host:test3.localhost AND Path:/test are matched.

You can also use the notation using a ; separator, same result:

  [frontends.frontend3]
  backend = "backend2"
    [frontends.frontend3.routes.test_1]
    rule = "Host:test3.localhost;Path:/test"

Finally, you can create a rule to bind multiple domains or Path to a frontend, using the , separator:

 [frontends.frontend2]
    [frontends.frontend2.routes.test_1]
    rule = "Host:test1.localhost,test2.localhost"
  [frontends.frontend3]
  backend = "backend2"
    [frontends.frontend3.routes.test_1]
    rule = "Path:/test1,/test2"

Rules Order

When combining Modifier rules with Matcher rules, it is important to remember that Modifier rules ALWAYS apply after the Matcher rules.

The following rules are both Matchers and Modifiers, so the Matcher portion of the rule will apply first, and the Modifier will apply later.

• PathStrip
• PathStripRegex
• PathPrefixStrip
• PathPrefixStripRegex

Modifiers will be applied in a pre-determined order regardless of their order in the rule configuration section.

1. PathStrip
2. PathPrefixStrip
3. PathStripRegex
4. PathPrefixStripRegex
5. AddPrefix
6. ReplacePath

Priorities

By default, routes will be sorted (in descending order) using rules length (to avoid path overlap): - PathPrefix:/foo;Host:foo.com (length == 28) will be matched before PathPrefixStrip:/foobar (length == 23) will be matched before PathPrefix:/foo,/bar (length == 20).
- A priority value of 0 will be ignored, so the default value will be calculated (rules length).

You can customize priority by frontend. The priority value override the rule length during sorting:

  [frontends]
    [frontends.frontend1]
    backend = "backend1"
    priority = 20
    passHostHeader = true
      [frontends.frontend1.routes.test_1]
      rule = "PathPrefix:/to"
    [frontends.frontend2]
    backend = "backend2"
    passHostHeader = true
      [frontends.frontend2.routes.test_1]
      rule = "PathPrefix:/toto"

Here, frontend1 will be matched before frontend2 (20 > 16).

Custom headers

Custom headers can be configured through the frontends, to add headers to either requests or responses that match the frontend's rules. This allows for setting headers such as X-Script-Name to be added to the request, or custom headers to be added to the response.

Warning

If the custom header name is the same as one header name of the request or response, it will be replaced.

In this example, all matches to the path /cheese will have the X-Script-Name header added to the proxied request and the X-Custom-Response-Header header added to the response.

[frontends]
  [frontends.frontend1]
  backend = "backend1"
    [frontends.frontend1.headers.customresponseheaders]
    X-Custom-Response-Header = "True"
    [frontends.frontend1.headers.customrequestheaders]
    X-Script-Name = "test"
    [frontends.frontend1.routes.test_1]
    rule = "PathPrefixStrip:/cheese"

In this second example, all matches to the path /cheese will have the X-Script-Name header added to the proxied request, the X-Custom-Request-Header header removed from the request, and the X-Custom-Response-Header header removed from the response.

[frontends]
  [frontends.frontend1]
  backend = "backend1"
    [frontends.frontend1.headers.customresponseheaders]
    X-Custom-Response-Header = ""
    [frontends.frontend1.headers.customrequestheaders]
    X-Script-Name = "test"
    X-Custom-Request-Header = ""
    [frontends.frontend1.routes.test_1]
    rule = "PathPrefixStrip:/cheese"

Security headers

Security related headers (HSTS headers, SSL redirection, Browser XSS filter, etc) can be added and configured per frontend in a similar manner to the custom headers above. This functionality allows for some easy security features to quickly be set.

An example of some of the security headers:

[frontends]
  [frontends.frontend1]
  backend = "backend1"
    [frontends.frontend1.headers]
    FrameDeny = true
    [frontends.frontend1.routes.test_1]
    rule = "PathPrefixStrip:/cheddar"
  [frontends.frontend2]
  backend = "backend2"
    [frontends.frontend2.headers]
    SSLRedirect = true
    [frontends.frontend2.routes.test_1]
    rule = "PathPrefixStrip:/stilton"

In this example, traffic routed through the first frontend will have the X-Frame-Options header set to DENY, and the second will only allow HTTPS request through, otherwise will return a 301 HTTPS redirect.

Note

The detailed documentation for those security headers can be found in unrolled/secure.

Backends

A backend is responsible to load-balance the traffic coming from one or more frontends to a set of http servers.

Servers

Servers are simply defined using a url. You can also apply a custom weight to each server (this will be used by load-balancing).

Note

Paths in url are ignored. Use Modifier to specify paths instead.

Here is an example of backends and servers definition:

[backends]
  [backends.backend1]
    # ...
    [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.backend2.servers.server1]
    url = "https://172.17.0.4:443"
    weight = 1
    [backends.backend2.servers.server2]
    url = "https://172.17.0.5:443"
    weight = 2
  [backends.backend3]
    # ...
    [backends.backend3.servers.server1]
    url = "h2c://172.17.0.6:80"
    weight = 1

• Two backends are defined: backend1 and backend2
• backend1 will forward the traffic to two servers: 172.17.0.2:80 with weight 10 and 172.17.0.3:80 with weight 1.
• backend2 will forward the traffic to two servers: 172.17.0.4:443 with weight 1 and 172.17.0.5:443 with weight 2 both using TLS.
• backend3 will forward the traffic to: 172.17.0.6:80 with weight 1 using HTTP2 without TLS.

Load-balancing

Various methods of load-balancing are supported:

• wrr: Weighted Round Robin.
• drr: Dynamic Round Robin: increases weights on servers that perform better than others. It also rolls back to original weights if the servers have changed.

Circuit breakers

A circuit breaker can also be applied to a backend, preventing high loads on failing servers. Initial state is Standby. CB observes the statistics and does not modify the request. In case the condition matches, CB enters Tripped state, where it responds with predefined code or redirects to another frontend. Once Tripped timer expires, CB enters Recovering state and resets all stats. In case the condition does not match and recovery timer expires, CB enters Standby state.

It can be configured using:

• Methods: LatencyAtQuantileMS, NetworkErrorRatio, ResponseCodeRatio
• Operators: AND, OR, EQ, NEQ, LT, LE, GT, GE

For example:

• NetworkErrorRatio() > 0.5: watch error ratio over 10 second sliding window for a frontend.
• LatencyAtQuantileMS(50.0) > 50: watch latency at quantile in milliseconds.
• ResponseCodeRatio(500, 600, 0, 600) > 0.5: ratio of response codes in ranges [500-600) and [0-600).

Here is an example of backends and servers definition:

[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

• backend1 will forward the traffic to two servers: http://172.17.0.2:80" with weight 10 and http://172.17.0.3:80 with weight 1 using default wrr load-balancing strategy.
• a circuit breaker is added on backend1 using the expression NetworkErrorRatio() > 0.5: watch error ratio over 10 second sliding window

Maximum connections

To proactively prevent backends from being overwhelmed with high load, a maximum connection limit can also be applied to each backend.

Maximum connections can be configured by specifying an integer value for maxconn.amount and maxconn.extractorfunc which is a strategy used to determine how to categorize requests in order to evaluate the maximum connections.

For example:

[backends]
  [backends.backend1]
    [backends.backend1.maxconn]
       amount = 10
       extractorfunc = "request.host"
   # ...

• backend1 will return HTTP code 429 Too Many Requests if there are already 10 requests in progress for the same Host header.
• Another possible value for extractorfunc is client.ip which will categorize requests based on client source ip.
• Lastly extractorfunc can take the value of request.header.ANY_HEADER which will categorize requests based on ANY_HEADER that you provide.

Sticky sessions

Sticky sessions are supported with both load balancers.
When sticky sessions are enabled, a cookie is set on the initial request. The default cookie name is an abbreviation of a sha1 (ex: _1d52e). On subsequent requests, the client will be directed to the backend stored in the cookie if it is still healthy. If not, a new backend will be assigned.

[backends]
  [backends.backend1]
    # Enable sticky session
    [backends.backend1.loadbalancer.stickiness]

    # Customize the cookie name
    #
    # Optional
    # Default: a sha1 (6 chars)
    #
    #  cookieName = "my_cookie"

    # Customize secure option
    #
    # Optional
    # Default: false
    #
    #  secure = true

    # Customize http only option
    #
    # Optional
    # Default: false
    #
    #  httpOnly = true

    # Customize same site option.
    # Can be: "none", "lax", "strict"
    #
    # Optional
    #
    #  sameSite = "none"

The deprecated way:

[backends]
  [backends.backend1]
    [backends.backend1.loadbalancer]
      sticky = true

Health Check

A health check can be configured in order to remove a backend from LB rotation as long as it keeps returning HTTP status codes other than 2xx or 3xx to HTTP GET requests periodically carried out by Traefik.
The check is defined by a path appended to the backend URL and an interval (given in a format understood by time.ParseDuration) specifying how often the health check should be executed (the default being 30 seconds). Each backend must respond to the health check within 5 seconds.
By default, the port of the backend server is used, however, this may be overridden.

A recovering backend returning 2xx or 3xx responses again is being returned to the LB rotation pool.

For example:

[backends]
  [backends.backend1]
    [backends.backend1.healthcheck]
    path = "/health"
    interval = "10s"

To use a different port for the health check:

[backends]
  [backends.backend1]
    [backends.backend1.healthcheck]
    path = "/health"
    interval = "10s"
    port = 8080

To use a different scheme for the health check:

[backends]
  [backends.backend1]
    [backends.backend1.healthcheck]
    path = "/health"
    interval = "10s"
    scheme = "http"

Additional http headers and hostname to health check request can be specified, for instance:

[backends]
  [backends.backend1]
    [backends.backend1.healthcheck]
    path = "/health"
    interval = "10s"
    hostname = "myhost.com"
    port = 8080
      [backends.backend1.healthcheck.headers]
      My-Custom-Header = "foo"
      My-Header = "bar"

Configuration

Traefik's configuration has two parts:

• The static Traefik configuration which is loaded only at the beginning.
• The dynamic Traefik configuration which can be hot-reloaded (no need to restart the process).

Static Traefik configuration

The static configuration is the global configuration which is setting up connections to configuration backends and entrypoints.

Traefik can be configured using many configuration sources with the following precedence order. Each item takes precedence over the item below it:

• Key-value store
• Arguments
• Configuration file
• Default

It means that arguments override configuration file, and key-value store overrides arguments.

Note

the provider-enabling argument parameters (e.g., --docker) set all default values for the specific provider.
It must not be used if a configuration source with less precedence wants to set a non-default provider value.

Configuration file

By default, Traefik will try to find a traefik.toml in the following places:

• /etc/traefik/
• $HOME/.traefik/
• . the working directory

You can override this by setting a configFile argument:

traefik --configFile=foo/bar/myconfigfile.toml

Please refer to the global configuration section to get documentation on it.

Arguments

Each argument (and command) is described in the help section:

traefik --help

Note that all default values will be displayed as well.

Key-value stores

Traefik supports several Key-value stores:

• Consul
• etcd
• ZooKeeper
• boltdb

Please refer to the User Guide Key-value store configuration section to get documentation on it.

Dynamic Traefik configuration

The dynamic configuration concerns :

• Frontends
• Backends
• Servers
• HTTPS Certificates

Traefik can hot-reload those rules which could be provided by multiple configuration backends.

We only need to enable watch option to make Traefik watch configuration backend changes and generate its configuration automatically. Routes to services will be created and updated instantly at any changes.

Please refer to the configuration backends section to get documentation on it.

Commands

traefik

Usage:

traefik [command] [--flag=flag_argument]

List of Traefik available commands with description :

• version : Print version
• storeconfig : Store the static Traefik configuration into a Key-value stores. Please refer to the Store Traefik configuration section to get documentation on it.
• bug: The easiest way to submit a pre-filled issue.
• healthcheck: Calls Traefik /ping to check health.

Each command may have related flags.

All those related flags will be displayed with :

traefik [command] --help

Each command is described at the beginning of the help section:

traefik --help

# or

docker run traefik[:version] --help
# ex: docker run traefik:1.5 --help

Command: bug

Here is the easiest way to submit a pre-filled issue on Traefik GitHub.

traefik bug

Watch this demo.

Command: healthcheck

This command allows to check the health of Traefik. Its exit status is 0 if Traefik is healthy and 1 if it is unhealthy.

This can be used with Docker HEALTHCHECK instruction or any other health check orchestration mechanism.

Note

The ping must be enabled to allow the healthcheck command to call /ping.

traefik healthcheck

OK: http://:8082/ping

Collected Data

This feature is disabled by default.

You can read the public proposal on this topic here.

Why ?

In order to help us learn more about how Traefik is being used and improve it, we collect anonymous usage statistics from running instances. Those data help us prioritize our developments and focus on what's more important (for example, which configuration backend is used and which is not used).

What ?

Once a day (the first call begins 10 minutes after the start of Traefik), we collect:

• the Traefik version
• a hash of the configuration
• an anonymous version of the static configuration:
  • token, user name, password, URL, IP, domain, email, etc, are removed

Note

We do not collect the dynamic configuration (frontends & backends).

Note

We do not collect data behind the scenes to run advertising programs or to sell such data to third-party.

Here is an example

• Source configuration:

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

[api]

[Docker]
  endpoint = "tcp://10.10.10.10:2375"
  domain = "foo.bir"
  exposedByDefault = true
  swarmMode = true

  [Docker.TLS]
    ca = "dockerCA"
    cert = "dockerCert"
    key = "dockerKey"
    insecureSkipVerify = true

[ECS]
  domain = "foo.bar"
  exposedByDefault = true
  clusters = ["foo-bar"]
  region = "us-west-2"
  accessKeyID = "AccessKeyID"
  secretAccessKey = "SecretAccessKey"

• Obfuscated and anonymous configuration:

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

[api]

[Docker]
  endpoint = "xxxx"
  domain = "xxxx"
  exposedByDefault = true
  swarmMode = true

  [Docker.TLS]
    ca = "xxxx"
    cert = "xxxx"
    key = "xxxx"
    insecureSkipVerify = false

[ECS]
  domain = "xxxx"
  exposedByDefault = true
  clusters = []
  region = "us-west-2"
  accessKeyID = "xxxx"
  secretAccessKey = "xxxx"

Show me the code !

If you want to dig into more details, here is the source code of the collecting system: collector.go

By default we anonymize all configuration fields, except fields tagged with export=true.

How to enable this ?

You can enable the collecting system by:

• adding this line in the configuration TOML file:

# Send anonymous usage data
#
# Optional
# Default: false
#
sendAnonymousUsage = true

• adding this flag in the CLI:

./traefik --sendAnonymousUsage=true