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zwoop pushed a commit to branch 9.0.x
in repository https://gitbox.apache.org/repos/asf/trafficserver.git
The following commit(s) were added to refs/heads/9.0.x by this push:
new 93ee51a PR#5867: Explain how to use open_con().
93ee51a is described below
commit 93ee51a65f0cef90be03d953b59066270619274f
Author: Oknet Xu <xuc...@skyguard.com.cn>
AuthorDate: Fri Aug 23 17:06:30 2019 +0800
PR#5867: Explain how to use open_con().
The DNS sub-system has 2 work modes:
- Primary-Secondary mode
- Round-Robin mode
The `open_con()` and `open_cons()` are shared with these 2 modes.
Within the Primary-Secondary mode:
- The `DNSHandler::ip` is used to store the Primary DNS server address.
- The `validate_ip()` is the API to load the first DNS server address
into The `DNSHandler::ip`.
- The `open_con()` is the API to update `DNSHandler::ip` with `target`
and connect to the address, but you cannot update `DNSHandler::ip` with
it self.
Within the Round-Robin mode:
- The `DNSHandler::ip` is useless.
- The `open_con()` is the API to connect to `target`.
The SplitDNS is only available in the Primary-Secondary mode:
- I suspect that the Round-Robin mode is a feature that was added later.
- The author only made this functionality for the DNS sub-system, and
forgot to do it for SplitDNS.
(cherry picked from commit 678ab7a778d66f83475b478868f254aa62ff8344)
---
iocore/dns/DNS.cc | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)
diff --git a/iocore/dns/DNS.cc b/iocore/dns/DNS.cc
index 8d91744..6713003 100644
--- a/iocore/dns/DNS.cc
+++ b/iocore/dns/DNS.cc
@@ -468,6 +468,15 @@ DNSHandler::open_cons(sockaddr const *target, bool failed,
int icon)
Open (and close) connections as necessary and also assures that the
epoll fd struct is properly updated.
+ target == nullptr :
+ open connection to DNSHandler::ip.
+ generally, the icon should be 0 if target == nullptr.
+
+ target != nullptr and icon == 0 :
+ open connection to target, and the target is assigned to DNSHandler::ip.
+
+ target != nullptr and icon > 0 :
+ open connection to target.
*/
void
DNSHandler::open_con(sockaddr const *target, bool failed, int icon, bool
over_tcp)
@@ -475,6 +484,8 @@ DNSHandler::open_con(sockaddr const *target, bool failed,
int icon, bool over_tc
ip_port_text_buffer ip_text;
PollDescriptor *pd = get_PollDescriptor(dnsProcessor.thread);
+ ink_assert(target != &ip.sa);
+
if (!icon && target) {
ats_ip_copy(&ip, target);
} else if (!target) {
@@ -549,6 +560,12 @@ DNSHandler::startEvent(int /* event ATS_UNUSED */, Event
*e)
dns_handler_initialized = 1;
SET_HANDLER(&DNSHandler::mainEvent);
if (dns_ns_rr) {
+ /* Round Robin mode:
+ * Establish a connection to each DNS server to make it a connection
pool.
+ * For each DNS Request, a connection is picked up from the pool by
round robin method.
+ *
+ * The first DNS server is assigned to DNSHandler::ip within
open_con() function.
+ */
int max_nscount = m_res->nscount;
if (max_nscount > MAX_NAMED) {
max_nscount = MAX_NAMED;
@@ -565,6 +582,18 @@ DNSHandler::startEvent(int /* event ATS_UNUSED */, Event
*e)
}
dns_ns_rr_init_down = 0;
} else {
+ /* Primary - Secondary mode:
+ * Establish a connection to the Primary DNS server.
+ * It always send DNS requests to the Primary DNS server.
+ * If the Primary DNS server dies,
+ * - it will attempt to send DNS requests to the secondary DNS
server until the Primary DNS server is back.
+ * - and keep to detect the health of the Primary DNS server.
+ * If DNSHandler::recv_dns() got a valid DNS response from the Primary
DNS server,
+ * - it means that the Primary DNS server returns.
+ * - it send all DNS requests to the Primary DNS server.
+ *
+ * The first DNS server is the Primary DNS server, and it is assigned
to DNSHandler::ip within validate_ip() function.
+ */
open_cons(nullptr); // use current target address.
n_con = 1;
}
@@ -587,8 +616,8 @@ DNSHandler::startEvent_sdns(int /* event ATS_UNUSED */,
Event *e)
this->validate_ip();
SET_HANDLER(&DNSHandler::mainEvent);
- open_cons(&ip.sa, false, n_con);
- ++n_con; // TODO should n_con be zeroed?
+ open_cons(nullptr, false, 0);
+ n_con = 1;
return EVENT_CONT;
}
@@ -647,7 +676,7 @@ DNSHandler::try_primary_named(bool reopen)
if (reopen && ((t - last_primary_reopen) > DNS_PRIMARY_REOPEN_PERIOD)) {
Debug("dns", "try_primary_named: reopening primary DNS connection");
last_primary_reopen = t;
- open_cons(&ip.sa, true, 0);
+ open_cons(nullptr, true, 0);
}
if ((t - last_primary_retry) > DNS_PRIMARY_RETRY_PERIOD) {
unsigned char buffer[MAX_DNS_REQUEST_LEN];
