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Diffstat (limited to 'doc/design-thoughts/backends.txt')
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diff --git a/doc/design-thoughts/backends.txt b/doc/design-thoughts/backends.txt new file mode 100644 index 0000000..d2474ce --- /dev/null +++ b/doc/design-thoughts/backends.txt @@ -0,0 +1,125 @@ +There has been a lot of confusion during the development because of the +backends and frontends. + +What we want : + +- being able to still use a listener as it has always been working + +- being able to write a rule stating that we will *change* the backend when we + match some pattern. Only one jump is allowed. + +- being able to write a "use_filters_from XXX" line stating that we will ignore + any filter in the current listener, and that those from XXX will be borrowed + instead. A warning would be welcome for options which will silently get + masked. This is used to factor configuration. + +- being able to write a "use_backend_from XXX" line stating that we will ignore + any server and timeout config in the current listener, and that those from + XXX will be borrowed instead. A warning would be welcome for options which + will silently get masked. This is used to factor configuration. + + + +Example : +--------- + + | # frontend HTTP/80 + | listen fe_http 1.1.1.1:80 + | use_filters_from default_http + | use_backend_from appli1 + | + | # frontend HTTPS/443 + | listen fe_https 1.1.1.1:443 + | use_filters_from default_https + | use_backend_from appli1 + | + | # frontend HTTP/8080 + | listen fe_http-dev 1.1.1.1:8080 + | reqadd "X-proto: http" + | reqisetbe "^Host: www1" appli1 + | reqisetbe "^Host: www2" appli2 + | reqisetbe "^Host: www3" appli-dev + | use_backend_from appli1 + | + | + | # filters default_http + | listen default_http + | reqadd "X-proto: http" + | reqisetbe "^Host: www1" appli1 + | reqisetbe "^Host: www2" appli2 + | + | # filters default_https + | listen default_https + | reqadd "X-proto: https" + | reqisetbe "^Host: www1" appli1 + | reqisetbe "^Host: www2" appli2 + | + | + | # backend appli1 + | listen appli1 + | reqidel "^X-appli1:.*" + | reqadd "Via: appli1" + | balance roundrobin + | cookie app1 + | server srv1 + | server srv2 + | + | # backend appli2 + | listen appli2 + | reqidel "^X-appli2:.*" + | reqadd "Via: appli2" + | balance roundrobin + | cookie app2 + | server srv1 + | server srv2 + | + | # backend appli-dev + | listen appli-dev + | reqadd "Via: appli-dev" + | use_backend_from appli2 + | + | + + +Now we clearly see multiple things : +------------------------------------ + + - a frontend can EITHER have filters OR reference a use_filter + + - a backend can EITHER have servers OR reference a use_backend + + - we want the evaluation to cross TWO levels per request. When a request is + being processed, it keeps track of its "frontend" side (where it came + from), and of its "backend" side (where the server-side parameters have + been found). + + - the use_{filters|backend} have nothing to do with how the request is + decomposed. + + +Conclusion : +------------ + + - a proxy is always its own frontend. It also has 2 parameters : + - "fi_prm" : pointer to the proxy holding the filters (itself by default) + - "be_prm" : pointer to the proxy holding the servers (itself by default) + + - a request has a frontend (fe) and a backend (be). By default, the backend + is initialized to the frontend. Everything related to the client side is + accessed through ->fe. Everything related to the server side is accessed + through ->be. + + - request filters are first called from ->fe then ->be. Since only the + filters can change ->be, it is possible to iterate the filters on ->be + only and stop when ->be does not change anymore. + + - response filters are first called from ->be then ->fe IF (fe != be). + + +When we parse the configuration, we immediately configure ->fi and ->be for +all proxies. + +Upon session creation, s->fe and s->be are initialized to the proxy. Filters +are executed via s->fe->fi_prm and s->be->fi_prm. Servers are found in +s->be->be_prm. + |