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replica redirect read&write to master in standalone mode #325

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replica redirect read&write to master in standalone mode #325

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8fce41e
replica redirect read&write to master in standalone mode
soloestoy Apr 16, 2024
0d83765
change to REDIRECT
soloestoy Apr 22, 2024
15163c9
Merge remote-tracking branch 'upstream/unstable' into replica-redirect
soloestoy May 9, 2024
be838bc
redirect by per client's capability
soloestoy May 16, 2024
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8 changes: 0 additions & 8 deletions src/cluster.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1461,20 +1461,12 @@ void askingCommand(client *c) {
* In this mode slaves will not redirect clients as long as clients access
* with read-only commands to keys that are served by the slave's master. */
void readonlyCommand(client *c) {
if (server.cluster_enabled == 0) {
addReplyError(c,"This instance has cluster support disabled");
return;
}
c->flags |= CLIENT_READONLY;
addReply(c,shared.ok);
}

/* The READWRITE command just clears the READONLY command state. */
void readwriteCommand(client *c) {
if (server.cluster_enabled == 0) {
addReplyError(c,"This instance has cluster support disabled");
return;
}
c->flags &= ~CLIENT_READONLY;
addReply(c,shared.ok);
}
1 change: 1 addition & 0 deletions src/config.c
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Expand Up @@ -3094,6 +3094,7 @@ standardConfig static_configs[] = {
createBoolConfig("replica-serve-stale-data", "slave-serve-stale-data", MODIFIABLE_CONFIG, server.repl_serve_stale_data, 1, NULL, NULL),
createBoolConfig("replica-read-only", "slave-read-only", DEBUG_CONFIG | MODIFIABLE_CONFIG, server.repl_slave_ro, 1, NULL, NULL),
createBoolConfig("replica-ignore-maxmemory", "slave-ignore-maxmemory", MODIFIABLE_CONFIG, server.repl_slave_ignore_maxmemory, 1, NULL, NULL),
createBoolConfig("replica-enable-redirect", NULL, MODIFIABLE_CONFIG, server.repl_replica_enable_redirect, 0, NULL, NULL),
createBoolConfig("jemalloc-bg-thread", NULL, MODIFIABLE_CONFIG, server.jemalloc_bg_thread, 1, NULL, updateJemallocBgThread),
createBoolConfig("activedefrag", NULL, DEBUG_CONFIG | MODIFIABLE_CONFIG, server.active_defrag_enabled, 0, isValidActiveDefrag, NULL),
createBoolConfig("syslog-enabled", NULL, IMMUTABLE_CONFIG, server.syslog_enabled, 0, NULL, NULL),
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11 changes: 11 additions & 0 deletions src/server.c
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Expand Up @@ -4009,6 +4009,17 @@ int processCommand(client *c) {
}
}

if (!server.cluster_enabled &&
server.masterhost &&
!mustObeyClient(c) &&
server.repl_replica_enable_redirect &&
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(is_write_command ||
(is_read_command && !(c->flags & CLIENT_READONLY)))) {
addReplyErrorSds(c,sdscatprintf(sdsempty(), "-MOVED -1 %s:%d",
server.masterhost, server.masterport));
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For cluster, we return the TLS port if the client is TLS and the non-TLS port if the client is non-TLS.

How can we handle this in standalone mode? Maybe we can only handle it if client connection and replication connection are both TLS or none of them is TLS? Otherwise return an error?

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Let's not coupling client connection and replication connection together (just like client connection and cluster bus). Maybe we need a new dedicated port to do the replicatlication, and this is a breaking change.

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@zuiderkwast yes, this is a problem if users use both TLS port and non-TLS port. And now in standalone mode replicas and master doesn't know the port's info each other.

Maybe we can use REPLCONF or something to send the port's info, I incline to open another issue to discuss it. I think it's better to discuss them separately to avoid mixing them up and making the problem more complicated.

At the beginning of TLS design, the server adopted a two port model, but many related issues were not well resolved. For example, cluster can provide two different services, TLS and non TLS, until redis/redis#12233 fixed by @CharlesChen888 . TLS is a more macro level issue I think.

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If we don't implement something now to to make the replica know both ports of the primary, then at least we should only use the redirect when the client can use it. Otherwise we should just return an error. We can't return a non-TLS port to a TLS client and vice versa.

Another problem that @enjoy-binbin pointed out is the announced-ip and announced-port. If they are in use, then probably the primary is using them too and the client can't use the redirect.

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@soloestoy soloestoy Apr 22, 2024 •
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The actual scenario is more complex, involving not only non-TLS and TLS port issues but also concerns regarding network isolation and NAT. There are four distinct scenarios in general:

  1. Both the client and the master/replica nodes are deployed in the same network, and both nodes utilize a single port (non-TLS or TLS port). In this case, replica and client access the master through the same port.
  2. Both the client and the master/replica nodes are deployed in the same network, and nodes provides two services ports (non-TLS and TLS port). In this situation, replica and client may access master's different ports.
  3. Client and master/replica nodes are deployed in separate networks. During this time the master/replica nodes need to provide service to client through NAT. Therefore, the master ip returned by REDIRECT also needs to be configured as the NAT IP.
  4. A more complex scenario involves the master and replica being deployed in separate networks as well. In this case, not only would the master/replica need to provide NAT IPs to the client, but they would also require additional NAT IPs for communication between themselves.

I understand all of these issues as we have encountered them in the production environment as well. We can thoroughly discuss these scenarios, but I would like to address the above issues step by step. I do not favor complicating things right from the start as it increases the complexity of engineering implementation.

This PR can resolve issue 1, achieving smooth switchover when it is within the same network and the same port. Then, we can proceed to solve the remaining issues.

return C_OK;
}

/* Disconnect some clients if total clients memory is too high. We do this
* before key eviction, after the last command was executed and consumed
* some client output buffer memory. */
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1 change: 1 addition & 0 deletions src/server.h
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Expand Up @@ -1911,6 +1911,7 @@ struct valkeyServer {
int repl_serve_stale_data; /* Serve stale data when link is down? */
int repl_slave_ro; /* Slave is read only? */
int repl_slave_ignore_maxmemory; /* If true slaves do not evict. */
int repl_replica_enable_redirect; /* If true replica would redirect read&write commands to master. */
time_t repl_down_since; /* Unix time at which link with master went down */
int repl_disable_tcp_nodelay; /* Disable TCP_NODELAY after SYNC? */
int slave_priority; /* Reported in INFO and used by Sentinel. */
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36 changes: 36 additions & 0 deletions tests/integration/replica-redirect.tcl
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@@ -0,0 +1,36 @@
start_server {tags {needs:repl external:skip}} {
start_server {} {
set master_host [srv -1 host]
set master_port [srv -1 port]

r replicaof $master_host $master_port
wait_for_condition 50 100 {
[s 0 master_link_status] eq {up}
} else {
fail "Replicas not replicating from master"
}

test {replica allow read command by default} {
r get foo
} {}

test {replica reply READONLY error for write command by default} {
assert_error {READONLY*} {r set foo bar}
}

test {replica redirect read and write command when enable replica-enable-redirect} {
r config set replica-enable-redirect yes
assert_error "MOVED -1 $master_host:$master_port" {r set foo bar}
assert_error "MOVED -1 $master_host:$master_port" {r get foo}
}

test {non-data access commands are not redirected} {
r ping
} {PONG}

test {replica allow read command in READONLY mode} {
r readonly
r get foo
} {}
}
}
12 changes: 12 additions & 0 deletions valkey.conf
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Expand Up @@ -817,6 +817,18 @@ replica-priority 100
# replica-announce-ip 5.5.5.5
# replica-announce-port 1234

# You can configure a replica instance to redirect data access commands
# to its master or not, excluding commands such as:
# INFO, AUTH, ROLE, SUBSCRIBE, UNSUBSCRIBE, PUBLISH.
#
# When enabled, a replica instance will reply "-MOVED -1 master-ip:port"
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Suggested change
# When enabled, a replica instance will reply "-MOVED -1 master-ip:port"
# When enabled, a replica instance will reply "-REDIRECT -1 master-ip:port"

# for data access commands. Normally these are write or read commands, if
# you want to run read commands while replica-enable-redirect is enabled,
# use the READONLY command first.
#
# This config only takes effect in standalone mode.
replica-enable-redirect no

############################### KEYS TRACKING #################################

# The client side caching of values is assisted via server-side support.
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