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MINOR: proxy: add option idle-close-on-response 

Avoid closing idle connections if a soft stop is in progress.

By default, idle connections will be closed during a soft stop. In some
environments, a client talking to the proxy may have prepared some idle
connections in order to send requests later. If there is no proper retry
on write errors, this can result in errors while haproxy is reloading.
Even though a proper implementation should retry on connection/write
errors, this option was introduced to support back compat with haproxy <
v2.4. Indeed before v2.4, we were waiting for a last request to be able
to add a "connection: close" header and advice the client to close the
connection.

In a real life example, this behavior was seen in AWS using the ALB in
front of a haproxy. The end result was ALB sending 502 during haproxy
reloads.
This patch was tested on haproxy v2.4, with a regular reload on the
process, and a constant trend of requests coming in. Before the patch,
we see regular 502 returned to the client; when activating the option,
the 502 disappear.

This patch should help fixing github issue #1506.
In order to unblock some v2.3 to v2.4 migraton, this patch should be
backported up to v2.4 branch.

Signed-off-by: William Dauchy <wdauchy@gmail.com>
[wt: minor edits to the doc to mention other options to care about]
Signed-off-by: Willy Tarreau <w@1wt.eu>
This commit is contained in:
William Dauchy 2022-01-05 22:53:24 +01:00 committed by Willy Tarreau
parent 6b6631593f
commit a9dd901143
4 changed files with 34 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
doc/configuration.txt
View File

@ -3756,6 +3756,7 @@ option tcp-smart-connect (*) X - X X
option tcpka X X X X
option tcplog X X X X
option transparent (*) X - X X
option idle-close-on-response (*) X X X -
external-check command X - X X
external-check path X - X X
persist rdp-cookie X - X X
@ -9015,6 +9016,35 @@ option external-check
See also : "external-check", "external-check command", "external-check path"
option idle-close-on-response
no option idle-close-on-response
Avoid closing idle frontend connections if a soft stop is in progress
May be used in sections : defaults | frontend | listen | backend
yes | yes | yes | no
Arguments : none
By default, idle connections will be closed during a soft stop. In some
environments, a client talking to the proxy may have prepared some idle
connections in order to send requests later. If there is no proper retry on
write errors, this can result in errors while haproxy is reloading. Even
though a proper implementation should retry on connection/write errors, this
option was introduced to support backwards compatibility with haproxy prior
to version 2.4. Indeed before v2.4, haproxy used to wait for a last request
and response to add a "connection: close" header before closing, thus
notifying the client that the connection would not be reusable.
In a real life example, this behavior was seen in AWS using the ALB in front
of a haproxy. The end result was ALB sending 502 during haproxy reloads.
Users are warned that using this option may increase the number of old
processes if connections remain idle for too long. Adjusting the client
timeouts and/or the "hard-stop-after" parameter accordingly might be
needed in case of frequent reloads.
See also: "timeout client", "timeout client-fin", "timeout http-request",
"hard-stop-after"
option log-health-checks
no option log-health-checks
Enable or disable logging of health checks status updates

2
include/haproxy/proxy-t.h
View File

@ -82,7 +82,7 @@ enum PR_SRV_STATE_FILE {
#define PR_O_REUSE_ALWS 0x0000000C /* always reuse a shared connection */
#define PR_O_REUSE_MASK 0x0000000C /* mask to retrieve shared connection preferences */
/* unused: 0x10 */
#define PR_O_IDLE_CLOSE_RESP 0x00000010 /* avoid closing idle connections during a soft stop */
#define PR_O_PREF_LAST 0x00000020 /* prefer last server */
#define PR_O_DISPATCH 0x00000040 /* use dispatch mode */
#define PR_O_FORCED_ID 0x00000080 /* proxy's ID was forced in the configuration */

3
src/mux_h1.c
View File

@ -2999,7 +2999,8 @@ static int h1_process(struct h1c * h1c)
*/
if (!(h1c->flags & H1C_F_IS_BACK)) {
if (unlikely(h1c->px->flags & (PR_FL_DISABLED|PR_FL_STOPPED))) {
if (h1c->flags & H1C_F_WAIT_NEXT_REQ)
if (!(h1c->px->options & PR_O_IDLE_CLOSE_RESP) &&
h1c->flags & H1C_F_WAIT_NEXT_REQ)
goto release;
}
}

1
src/proxy.c
View File

@ -70,6 +70,7 @@ const struct cfg_opt cfg_opts[] =
{ "dontlognull", PR_O_NULLNOLOG, PR_CAP_FE, 0, 0 },
{ "http-buffer-request", PR_O_WREQ_BODY, PR_CAP_FE | PR_CAP_BE, 0, PR_MODE_HTTP },
{ "http-ignore-probes", PR_O_IGNORE_PRB, PR_CAP_FE, 0, PR_MODE_HTTP },
{ "idle-close-on-response", PR_O_IDLE_CLOSE_RESP, PR_CAP_FE, 0, PR_MODE_HTTP },
{ "prefer-last-server", PR_O_PREF_LAST, PR_CAP_BE, 0, PR_MODE_HTTP },
{ "logasap", PR_O_LOGASAP, PR_CAP_FE, 0, 0 },
{ "nolinger", PR_O_TCP_NOLING, PR_CAP_FE | PR_CAP_BE, 0, 0 },