Varnish Processing States¶
Introduction¶
Varnish processing of client and backend requests is implemented as state machines. Whenever a state is entered, a C function is called, which in turn calls the appropriate Varnish core code functions to process the request or response at this stage. For most states, core code also calls into a state-specific function compiled from VCL, a VCL subroutine (see Built in subroutines ).
As a general guideline, core code aims to prepare objects accessible from VCL with good defaults for the most common cases before calling into the respective VCL subroutine. These can then be modified from VCL where necessary.
The following graphs attempt to provide an overview over the processing states, their transisions and the most relevant functions in core code. They represent a compromise between usefulness for core/VMOD developers and administrators and are intended to serve as the reference basis for deriavtive work, such as more VCL-centric views.
Client Side¶
![/*
* we should format labels in a readable form like
* label="\
* {cnt_deliver:|\
* Filter obj.-\>resp.|\
* {vcl_deliver\{\}|\
* {req.*|resp.*}}|\
* {restart|<deliver>deliver|<synth>synth}}"
*
* <rant>
* ... but some servers in the v-c.o build farm use old graphviz 2.26.3
* which cannot handle labels with additional whitespace properly, so
* for the time being we need to fall back into dark middle ages and
* use illegibly long lines
* </rant>
* -- slink 20141013
*/
digraph cache_req_fsm {
margin="0.25"
ranksep="0.5"
center="1"
//// XXX does this belong here? -- from cache_vcl.c
/*
vcl_load [label = "vcl.load",shape=plaintext]
vcl_load -> init
init [
shape=record
label="
{VCL_Load:|
{vcl_init}|
{<ok>ok|<fail>fail}}"
]
init:ok -> ok
init:fail -> fail
vcl_discard [label = "vcl.discard",shape=plaintext]
vcl_discard -> fini
fini [
shape=record
label="
{VCL_Nuke:|
{vcl_fini}|
{<ok>ok}}"
]
fini:ok -> ok
*/
acceptor [
shape=hexagon
label="Request received"
]
ESI_REQ [ shape=hexagon ]
RESTART [shape=plaintext]
ESI_REQ -> recv
SYNTH [shape=plaintext]
acceptor -> recv [style=bold]
subgraph xcluster_deliver {
/* cnt_deliver() */
deliver [
shape=record
label="{cnt_deliver:|Filter obj.-\>resp.|{vcl_deliver\{\}|{req.*|resp.*}}|{restart|<deliver>deliver|<synth>synth}}"
]
deliver:deliver:s -> V1D_Deliver [style=bold,color=green]
deliver:deliver:s -> V1D_Deliver [style=bold,color=red]
deliver:deliver:s -> V1D_Deliver [style=bold,color=blue]
stream [label="stream?\nbody",style=filled,color=turquoise]
stream -> V1D_Deliver [style=dotted]
}
V1D_Deliver -> DONE
/* cnt_synth() */
subgraph xcluster_synth {
synth [
shape=record
label="{cnt_synth:|{vcl_synth\{\}|{req.*|resp.*}}|{<del>deliver|<restart>restart}}"
]
SYNTH -> synth [color=purple]
synth:del:s -> V1D_Deliver [color=purple]
}
subgraph cluster_backend {
style=filled
color=aliceblue
"see backend graph" [shape=plaintext]
node [shape=box,
style=filled,
color=turquoise]
BGFETCH
FETCH
FETCH_DONE
FETCH_FAIL
}
lookup2:deliver:s -> BGFETCH [label="parallel\nif obj expired",
color=green]
FETCH_FAIL -> synth [color=purple]
FETCH_DONE -> deliver [style=bold,color=red]
FETCH_DONE -> deliver [style=bold,color=blue]
FETCH -> FETCH_DONE [style=dotted]
FETCH -> FETCH_FAIL [style=dotted]
/* cnt_lookup() */
subgraph xcluster_lookup {
lookup [
shape=record
color=grey
fontcolor=grey
label="{<top>cnt_lookup:|hash lookup|{<h>hit?|<miss>miss?|<hfp>hit-for-pass?|<busy>busy?}}"
]
lookup2 [
shape=record
label="{<top>cnt_lookup:|{vcl_hit\{\}|{req.*|obj.*}}|{<deliver>deliver|<fetch>fetch|restart|synth|<pass>pass}}"
]
}
lookup:busy:e -> lookup:top:e [label="(waitinglist)",
color=grey,
fontcolor=grey]
lookup:miss:s -> miss [style=bold,color=blue]
lookup:hfp:s -> pass [style=bold,color=red]
lookup:h:s -> lookup2 [style=bold,color=green]
lookup2:deliver:s -> deliver:n [style=bold,color=green]
lookup2:fetch:s -> miss [style=bold,color=blue]
// XXX should not happen
// lookup2:fetch:s -> pass [style=bold,color=red,label="(no busy obj)"]
lookup2:pass:s -> pass [style=bold,color=red]
/* cnt_miss */
subgraph xcluster_miss {
miss [
shape=record
label="{cnt_miss:|{vcl_miss\{\}|req.*}|{<fetch>fetch|<synth>synth|<rst>restart|<pass>pass}}"
]
}
miss:fetch:s -> FETCH [style=bold,color=blue]
miss:pass:s -> pass [style=bold,color=red]
/* cnt_pass */
subgraph xcluster_pass {
pass [
shape=record
label="{cnt_pass:|{vcl_pass\{\}|req.*}|{<fetch>fetch|<synth>synth|<rst>restart}}"
]
}
pass:fetch:s -> FETCH [style=bold, color=red]
/* cnt_pipe */
subgraph xcluster_pipe {
pipe [
shape=record
label="{cnt_pipe:|filter req.*-\>bereq.*|{vcl_pipe\{\}|{req.*|bereq.*}}|{<pipe>pipe|<synth>synth}}"
]
pipe_do [
shape=ellipse
label="send bereq,\ncopy bytes until close"
]
pipe:pipe -> pipe_do [style=bold,color=orange]
}
pipe_do -> DONE [style=bold,color=orange]
/* cnt_restart */
subgraph xcluster_restart {
restart [
shape=record
color=grey
fontcolor=grey
label="{cnt_restart:|{<ok>ok?|<max>max_restarts?}}"
]
}
RESTART -> restart [color=purple]
restart:ok:s -> recv
restart:max:s -> err_restart [color=purple]
err_restart [label="SYNTH",shape=plaintext]
/* cnt_recv() */
subgraph xcluster_recv {
recv [
shape=record
label="{cnt_recv:|{vcl_recv\{\}|req.*}|{<hash>hash|<purge>purge|<pass>pass|<pipe>pipe|<synth>synth}}"
]
recv:hash -> hash [style=bold,color=green]
hash [
shape=record
label="{cnt_recv:|{vcl_hash\{\}|req.*}|{<lookup>lookup}}"
]
}
recv:pipe -> pipe [style=bold,color=orange]
recv:pass -> pass [style=bold,color=red]
hash:lookup:w -> lookup [style=bold,color=green]
hash:lookup:s -> purge:top:n [style=bold,color=purple]
recv:purge:s -> hash [style=bold,color=purple]
/* cnt_purge */
subgraph xcluster_purge {
purge [
shape=record
label="{<top>cnt_purge:|{vcl_purge\{\}|req.*}|{<synth>synth|<restart>restart}}"
]
}
}](../_images/graphviz-9ec354078058728757ad7b5c526a625ea90bba68.svg)
Backend Side¶
![/*
* we should format labels in a readable form like
* label="
* {vbf_stp_startfetch:|
* {vcl_backend_fetch\{\}|bereq.*}|
* {abandon|
* <fetch>fetch}}"
*
* <rant>
* ... but some servers in the v-c.o build farm use old graphviz 2.26.3
* which cannot handle labels with additional whitespace properly, so
* for the time being we need to fall back into dark middle ages and
* use illegibly long lines
* </rant>
* -- slink 20141013
*/
digraph cache_fetch {
margin="0.5"
center="1"
/*** cache_fetch.c ***/
subgraph cluster_backend {
style=filled
color=aliceblue
RETRY [shape=plaintext]
v_b_f_BGFETCH [label="BGFETCH",
shape=box,
style=filled,
color=turquoise]
v_b_f_FETCH [label="FETCH",
shape=box,
style=filled,
color=turquoise]
v_b_f_BGFETCH -> v_b_f [style=bold,color=green]
v_b_f_FETCH -> v_b_f [style=bold,color=blue]
v_b_f_FETCH -> v_b_f [style=bold,color=red]
RETRY -> v_b_f [color=purple]
/* vbf_stp_startfetch() */
v_b_f [
shape=record
label="{vbf_stp_startfetch:|{vcl_backend_fetch\{\}|bereq.*}|{abandon|<fetch>fetch}}"
]
v_b_f:fetch:s -> v_b_hdrs [style=bold]
v_b_hdrs [ label="send bereq,\nread beresp (headers)"]
v_b_hdrs -> v_b_r [style=bold]
v_b_hdrs -> v_b_e
v_b_r [
shape=record
label="{vbf_stp_startfetch:|{vcl_backend_response\{\}|{bereq.*|beresp.*}}|{{retry|{<max>max?|<retry>ok?}}|abandon|{deliver|{<fetch_304>304?|<non_304>other?}}}}"
]
v_b_r:retry -> v_b_r_retry [color=purple]
v_b_r:max -> v_b_e
v_b_r:fetch_304:s -> vbf_stp_condfetch
v_b_r:non_304:s -> vbf_stp_fetch
v_b_r_retry [label="RETRY",shape=plaintext]
vbf_stp_fetch [
shape=record
fontcolor=grey
color=grey
label="{vbf_stp_fetch:|setup VFPs|<fetch>fetch|{fetch_fail?|error?|<ok>ok?}}"
]
vbf_stp_fetch:ok:s -> FETCH_DONE
vbf_stp_condfetch [
shape=record
fontcolor=grey
color=grey
label="{vbf_stp_condfetch:|copy obj attr|steal body|{fetch_fail?|<ok>ok?}}"
]
vbf_stp_condfetch:ok:s -> FETCH_DONE
error [shape=plaintext]
error -> FETCH_FAIL
/* vbf_stp_error */
v_b_e [
shape=record
label="{vbf_stp_error:|{vcl_backend_error\{\}|{bereq.*|beresp.*}}|{{retry|{<max>max?|<retry>ok?}}|<deliver>deliver}}}"
]
// v_b_e:deliver aka "backend synth" - goes into cache
v_b_e:deliver -> FETCH_DONE [label="\"backend synth\""]
v_b_e:retry -> v_b_e_retry [color=purple]
v_b_e_retry [label="RETRY",shape=plaintext]
v_b_e:max:s -> FETCH_FAIL
v_b_e_retry [label="RETRY",shape=plaintext]
FETCH_DONE [label="FETCH_DONE",
shape=box,style=filled,color=turquoise]
abandon [shape=plaintext]
abandon -> FETCH_FAIL
// F_STP_FAIL
FETCH_FAIL [label="FETCH_FAIL",
shape=box,style=filled,color=turquoise]
}
}](../_images/graphviz-241192ee56882b0a2b2d321512afc1f917e7d3df.svg)