title: what are backend and frontend in traefik.toml
body: <p>While reading the Documents of Traefik I was confused when I face the configuration skeleton that was mentioned in <a href="https://docs.traefik.io/configuration/backends/file/" rel="nofollow noreferrer">the documentation</a>:</p>
  
  <p>traefik.toml:</p>
  
  <pre><code>defaultEntryPoints = ["http", "https"]
  
  [entryPoints]
    [entryPoints.http]
      # ...
    [entryPoints.https]
      # ...
  
  [file]
  
  # rules
  [backends]
    [backends.backend1]
      # ...
    [backends.backend2]
      # ...
  
  [frontends]
    [frontends.frontend1]
    # ...
    [frontends.frontend2]
    # ...
    [frontends.frontend3]
    # ...
  
  # HTTPS certificate
  [[tls]]
    # ...
  
  [[tls]]
    # ...
  </code></pre>
  
  <p>what is the reason behind dividing rule section in the configuration file into two different sub-sections as <code>backend</code> and <code>frontend</code>?</p>