Incomplete responses for some requests

Carl Alexander carlalexander at
Thu Sep 15 02:45:22 CEST 2016

Hi everyone,

I'm having a weird issue that I have no idea how to solve. I have a setup
where I have varnish sitting between two vhosts. An SSL termination proxy
which forwards requests to varnish who forwards them to a backend.

The setup works perfectly for 99% of pages. But, for certain pages, varnish
seems to choke and only returns part of the html response. This can happen
consistently or at random for the same page. It also varies between
browsers sometimes.

When digging into varnishlog, I can find this FetchError for the backend:

-   Fetch_Body     4 eof stream
-   FetchError     Resource temporarily unavailable
-   FetchError     eof socket fail
-   BackendClose   24 boot.webserver
-   BereqAcct      1274 0 1274 333 32554 32887
-   End

So I figured that maybe it's a nginx issue. When I turn on debug logs,
nginx tells me that it's varnish that closed the connection. It was never
able to send the complete html response back (that's probably why it's
truncated). Here's the nginx logs:

2016/09/14 23:49:08 [info] 24670#24670: *566 epoll_wait() reported that
client prematurely closed connection, so upstream connection is closed too
while reading upstream

So on one side, I have varnish saying that nginx became unavailable. And on
the other, I have nginx telling me that varnish closed the connection. I
don't know which one is right.

But if I remove varnish and send the proxy request to the backend directly,
everything works. So the signs seem to point to varnish, but I can't seem
to find what's causing this. It started on Varnish 4.1.1, but upgrading to
4.1.3 didn't change anything.

I'm also not sure how to troubleshoot this further. I tried to look at the
varnish source code. The FetchError is just a generic C error so I don't
have much else to go on.

I've also attached the output of "" below:

accept_filter              off [bool] (default)
acceptor_sleep_decay       0.9 (default)
acceptor_sleep_incr        0.000 [seconds] (default)
acceptor_sleep_max         0.050 [seconds] (default)
auto_restart               on [bool] (default)
backend_idle_timeout       60.000 [seconds] (default)
ban_dups                   on [bool] (default)
ban_lurker_age             60.000 [seconds] (default)
ban_lurker_batch           1000 (default)
ban_lurker_sleep           0.010 [seconds] (default)
between_bytes_timeout      60.000 [seconds] (default)
cc_command                 "exec gcc -std=gnu99 -g -O2 -fstack-protector
--param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall -Werror
-Wno-error=unused-result -pthread -fpic -shared -Wl,-x -o %o %s" (default)
cli_buffer                 8k [bytes] (default)
cli_limit                  48k [bytes] (default)
cli_timeout                60.000 [seconds] (default)
clock_skew                 10 [seconds] (default)
connect_timeout            3.500 [seconds] (default)
critbit_cooloff            180.000 [seconds] (default)
debug                      none (default)
default_grace              10.000 [seconds] (default)
default_keep               0.000 [seconds] (default)
default_ttl                3600.000 [seconds]
feature                    none (default)
fetch_chunksize            16k [bytes] (default)
fetch_maxchunksize         0.25G [bytes] (default)
first_byte_timeout         60.000 [seconds] (default)
gzip_buffer                32k [bytes] (default)
gzip_level                 6 (default)
gzip_memlevel              8 (default)
http_gzip_support          on [bool] (default)
http_max_hdr               64 [header lines] (default)
http_range_support         on [bool] (default)
http_req_hdr_len           8k [bytes] (default)
http_req_size              32k [bytes] (default)
http_resp_hdr_len          8k [bytes] (default)
http_resp_size             32k [bytes] (default)
idle_send_timeout          60.000 [seconds] (default)
listen_depth               1024 [connections] (default)
lru_interval               2.000 [seconds] (default)
max_esi_depth              5 [levels] (default)
max_restarts               4 [restarts] (default)
max_retries                4 [retries] (default)
nuke_limit                 50 [allocations] (default)
pcre_match_limit           10000 (default)
pcre_match_limit_recursion 20 (default)
ping_interval              3 [seconds] (default)
pipe_timeout               60.000 [seconds] (default)
pool_req                   10,100,10 (default)
pool_sess                  10,100,10 (default)
pool_vbo                   10,100,10 (default)
prefer_ipv6                off [bool] (default)
rush_exponent              3 [requests per request] (default)
send_timeout               600.000 [seconds] (default)
session_max                100000 [sessions] (default)
shm_reclen                 255b [bytes] (default)
shortlived                 10.000 [seconds] (default)
sigsegv_handler            on [bool] (default)
syslog_cli_traffic         on [bool] (default)
tcp_fastopen               off [bool] (default)
tcp_keepalive_intvl        75.000 [seconds] (default)
tcp_keepalive_probes       9 [probes] (default)
tcp_keepalive_time         7200.000 [seconds] (default)
thread_pool_add_delay      0.000 [seconds] (default)
thread_pool_destroy_delay  1.000 [seconds] (default)
thread_pool_fail_delay     0.200 [seconds] (default)
thread_pool_max            5000 [threads] (default)
thread_pool_min            100 [threads] (default)
thread_pool_stack          48k [bytes] (default)
thread_pool_timeout        300.000 [seconds] (default)
thread_pools               2 [pools] (default)
thread_queue_limit         20 (default)
thread_stats_rate          10 [requests] (default)
timeout_idle               5.000 [seconds] (default)
timeout_linger             0.050 [seconds] (default)
vcc_allow_inline_c         off [bool] (default)
vcc_err_unref              on [bool] (default)
vcc_unsafe_path            on [bool] (default)
vcl_cooldown               600.000 [seconds] (default)
vcl_dir                    /etc/varnish (default)
vmod_dir                   /usr/lib/varnish/vmods (default)
vsl_buffer                 4k [bytes] (default)
vsl_mask                   -VCL_trace,-WorkThread,-Hash,-VfpAcct (default)
vsl_reclen                 255b [bytes] (default)
vsl_space                  80M [bytes] (default)
vsm_free_cooldown          60.000 [seconds] (default)
vsm_space                  1M [bytes] (default)
workspace_backend          64k [bytes] (default)
workspace_client           64k [bytes] (default)
workspace_session          0.50k [bytes] (default)
workspace_thread           2k [bytes] (default)

Thanks in advance for any help,
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