upstream - behavior on pool exhaustion
Ruslan Ermilov
ru at nginx.com
Thu May 18 11:12:04 UTC 2017
Did you have a chance to try my patch yet?
On Tue, Apr 25, 2017 at 05:44:37PM +0300, Ruslan Ermilov wrote:
> On Sat, Apr 22, 2017 at 01:52:48AM +0200, B.R. via nginx wrote:
> > I do not know if your detailed explanation was aimed to me, or to the list
> > in general, but I got all that already as far as I am concerned.
> >
> > To me, when an attempt is made to an upstream group where no peer can be
> > selected, a 502 should be returned for that request, and no upstream having
> > been selected, no $upstream_* variable should contain anything. An error
> > message should be generated in the error log.
> > I fail to see the benefit of having the group name being considered as an
> > upstream peer.... For cons, that name might get confused with a domain
> > name, and the grammar of the $upstream_addr variable is complexified.
> > Not that, as stated before, the docs merely say the $upstream_addr should
> > contains IP addresses and ports of peers, no mention of the upstream group
> > name there.
> >
> > Well, it seems your design decisions are made, and even though I see things
> > differently, I understand what I did not get before.
> > Is my vision broke, ie some benefit I am failing to see about your
> > implementation?
>
> I agree with you that it's not logical, I was just trying to explain
> in details why it happens the way it is. I've prepared a patch that
> addresses this and other inconsistencies with $upstream_* variables.
> The only assertion I've preserved is that the number of elements
> always stays equal to the number of attempts made to select a peer.
> What this means for $upstream_addr is that instead of the upstream
> group name it'll now output `-' as one of the possible values, much
> like it's always the case for $upstream_status and $upstream_response_time
> (see the answer to your other question below).
>
> > Another linked question:
> > I got some cases in which $upstream_response_time was '-' for some peers
> > (and not a numeric value like 0.000).
> > What is the meaning of that? Connection failed? I am not logging the
> > $upstream_status variable, not $upstream_connect_time, thus have limited
> > information.
> > Could that '-' appear anywhere in the list?
>
> This happens when the client aborts the connection before the upstream
> server sends the status line with the status code. The same holds
> true for $upstream_status. And while it seems logical for $upstream_status
> not to output it when the status code is unknown, I see no reason not to
> output the actual time spent on obtaining the response in this case.
> The server may have responded with "HTTP/1.1 ", then $upstream_bytes_received
> will be 9, but $upstream_response_time is `-'. That's another inconsistency
> that my patch fixes.
>
> Also, $upstream_status no longer outputs 502 for the case when no live
> upstream could be selected. It'll similarly output `-' to mean "not
> applicable" (for this particular attempt).
>
> Just in case you want to give it a try, I've attached the patch against
> the current nginx version.
>
> diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
> --- a/src/http/ngx_http_upstream.c
> +++ b/src/http/ngx_http_upstream.c
> @@ -1481,6 +1481,7 @@ ngx_http_upstream_connect(ngx_http_reque
> u->state->response_time = ngx_current_msec;
> u->state->connect_time = (ngx_msec_t) -1;
> u->state->header_time = (ngx_msec_t) -1;
> + u->state->selected = 1;
>
> rc = ngx_event_connect_peer(&u->peer);
>
> @@ -1496,6 +1497,7 @@ ngx_http_upstream_connect(ngx_http_reque
> u->state->peer = u->peer.name;
>
> if (rc == NGX_BUSY) {
> + u->state->selected = 0;
> ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "no live upstreams");
> ngx_http_upstream_next(r, u, NGX_HTTP_UPSTREAM_FT_NOLIVE);
> return;
> @@ -4146,7 +4148,9 @@ ngx_http_upstream_next(ngx_http_request_
> return;
> }
>
> - u->state->status = status;
> + if (ft_type != NGX_HTTP_UPSTREAM_FT_NOLIVE) {
> + u->state->status = status;
> + }
>
> timeout = u->conf->next_upstream_timeout;
>
> @@ -5223,7 +5227,7 @@ ngx_http_upstream_addr_variable(ngx_http
>
> for (i = 0; i < r->upstream_states->nelts; i++) {
> if (state[i].peer) {
> - len += state[i].peer->len + 2;
> + len += (state[i].selected ? state[i].peer->len : 1) + 2;
>
> } else {
> len += 3;
> @@ -5241,7 +5245,13 @@ ngx_http_upstream_addr_variable(ngx_http
>
> for ( ;; ) {
> if (state[i].peer) {
> - p = ngx_cpymem(p, state[i].peer->data, state[i].peer->len);
> +
> + if (state[i].selected) {
> + p = ngx_cpymem(p, state[i].peer->data, state[i].peer->len);
> +
> + } else {
> + *p++ = '-';
> + }
> }
>
> if (++i == r->upstream_states->nelts) {
> @@ -5368,7 +5378,7 @@ ngx_http_upstream_response_time_variable
> state = r->upstream_states->elts;
>
> for ( ;; ) {
> - if (state[i].status) {
> + if (state[i].selected) {
>
> if (data == 1 && state[i].header_time != (ngx_msec_t) -1) {
> ms = state[i].header_time;
> @@ -5445,12 +5455,17 @@ ngx_http_upstream_response_length_variab
> state = r->upstream_states->elts;
>
> for ( ;; ) {
> -
> - if (data == 1) {
> - p = ngx_sprintf(p, "%O", state[i].bytes_received);
> + if (state[i].selected) {
> +
> + if (data == 1) {
> + p = ngx_sprintf(p, "%O", state[i].bytes_received);
> +
> + } else {
> + p = ngx_sprintf(p, "%O", state[i].response_length);
> + }
>
> } else {
> - p = ngx_sprintf(p, "%O", state[i].response_length);
> + *p++ = '-';
> }
>
> if (++i == r->upstream_states->nelts) {
> diff --git a/src/http/ngx_http_upstream.h b/src/http/ngx_http_upstream.h
> --- a/src/http/ngx_http_upstream.h
> +++ b/src/http/ngx_http_upstream.h
> @@ -65,6 +65,7 @@ typedef struct {
> off_t bytes_received;
>
> ngx_str_t *peer;
> + ngx_uint_t selected; /* unsigned selected:1 */
> } ngx_http_upstream_state_t;
>
>
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--
Ruslan Ermilov
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