The root problem this is attempting to address is sporadic
weird cases in which etcd mistakenly thinks it's down even when
it's up. I am not confident that this is addressed, but there's
a reasonable chance that it is, and I can't trigger it at the
moment, but it was always sporadic, so that doesn't prove much.
There's a lot going on here, and it comes into roughly three
categories.
First: Dropping unused/unneeded code. There's a lot of leftover
bits from the initial development and refactoring of this.
Second: Unifying and shuffling some of the design. We had
multiple interfaces which are functionally impossible to
usefully implement separately, so they're combined together,
and in some cases, moved.
Third: Streamlining logic and simplifying design choices.
This is combined into one commit because the changes are
thoroughly entertwined with each other and you can't usefully
break most of them out.
Also, a bunch of test coverage for most of these changes.
Big changes:
We merge the topology and disco packages. The topology and disco
packages being separate creates a complicated tangle of problems
and dependencies. The fundamental problem, approximately, is that
topology.Node has to track disco.NodeState.
There's three core interfaces interacting here:
topology.Noder (maintains list of nodes)
disco.Stator (maintains the state of a node)
disco.Metadator (stores, possibly retrieves, node metadata)
But the node state mantained by the Noder *is* the set of node
metadata, plus state updates produced by Stators. The only actual
non-trivial and usable implementation of these interfaces is a single
thing which implements all three, and in which the implementations
share a single backend data source which they are all modifying.
But you can't move Noder into disco, because Noder has to refer
to topology.Node, but topology.Node refers to disco.
Solution: First, merge these two packages. Second, merge these
three interfaces, to provide a single interface which is more
clear about the fact that (metadator.)SetMetadata() and
(stator.)Started() are both changing the output we'll get from
(noder.)Nodes().
We rework the node state tracking.
We have this nodeStates map which is almost unused. Really, we
don't need it at all. Every node's state is either its last heartbeat
state or "Unknown", so we simplify this a bit. Also, we ensure that
the populateNodeStates function itself is yielding the sorted nodes
list, so we don't have to be as worried about possible later lookups
of sortedNodes happening outside a lock. We also add diagnostics
for deleting nodes from the metadata list (this should never happen),
and try to track heartbeat state more closely.
This is *probably* what fixes the underlying reported problem,
if anything did.
Still an open issue: Make heartbeat state changes aware of when
they're talking about *this* node and possibly not try to
mark it down? Except this may have a flaw: That would result in
each node disagreeing with other nodes in etcd about the state
of that node in the failure cases, and undermine the point of
using etcd to keep these states consistent.
We reduce the number of contexts and cancelfuncs in the etcd wrapper.
We create a shared context for the non-etcd.embed children of our
etcd wrapper, the heartbeat/keepalive and the node watcher, so we
can cancel that one context and cancel all of those at once, so
we don't need to separately track a function to call to cancel
the watch, AND be closing another channel. Also, our shutdown
now propagates automatically to the various etcd API calls we've
made for things like the node watcher and keepalive calls.
We still need to watch that channel in watchNodesOnce, though,
because apparently the watch doesn't yield an error even if the
context calling it is canceled. Whee.
This should reduce the risk of ending up in an inconsistent state,
and also the Close() function is probably idempotent now.
Smaller changes:
* Remove config-generators that existed to generate etcd
configs but were used only for tests that no longer exist
or make sense.
* Move the logic to generate etcd configs into the etcd
package, instead of the "testing" subpackage. This allows
us to write a self-contained config generator for
clusters where the nodes know about each other, but do
this just with etcd, not with full featurebase servers.
* Move the thing generating `fake:%d` socket names into
the etcd package, which is the only place we use it.
Also simplify it slightly.
* Don't panic on invalid URLs, report errors from them.
* At least try to use etcd's config.Validate functionality.
It's underdocumented, so we're not sure what it will report,
but at least if it does we'll get reports from it and
know what they are?
* Try to handle CompactRevision errors from watches more
correctly -- after a CompactRevision, any future attempt
to watch from a lower revision will necessarily fail, so
we adjust our target revision up. We don't have good
testing for this.
* Drop the Metadata() method (that used to be in Metadator)
because nothing ever used it and it didn't make much sense
to try.
* Convert SetMetadata from taking an arbitrary json blob
to taking the only data that would ever be valid since
we always use it to extract node information anyway.
* Drop several unused functions, unexport things only used
internally.
* Replace Started() with SetState("STARTED"), allowing us
to write tests that mess with states. We weren't really thinking
carefully about state transitions sometimes and now it's much
easier to do that thinking.
* Stop leaving stray localhost:2380 and localhost:2379 in
our embed config. We still sometimes see peer requests from
those and I honestly don't know why, but at least it should
be rarer.
We had two different, incompatible-with-each-other, and both
individually broken, partial implementations of resizing logic.
There's the original pre-etcd resize, and then the etcd resize,
and neither works, but there's conflicts between the ways they
don't work.
No attempt to fix this is likely to yield decent results, so
instead, we yank them both out entirely, so if we decide to
implement resizing (which we will) we won't be confused by
stray code pertaining to resizing that's not really hooked
up to anything.
We're leaving the resize messages in protobuf to avoid renumbering
protobuf messages. We rename some of our message types to UNUSED0,
etcetera, so that any code still using the old names won't
compile, to make sure we get rid of it, but we can't just drop
the numbers without breaking rolling restart.
The Resize_AddNode tests are removed not just because we don't
have resizing, but because they were completely broken anyway
and never worked at all. But there's no reason to fix them because
they exist to fix the functionality we didn't have and are now
removing the vestigial remains of.
We also drop the one usage of the AddNode function of Noder, because
it was used only by one test code fragment that was creatincg clusters,
and that can be done more correctly. There were no other call sites
at all.
We mark the monitorAntiEntropy function to be ignored by
code coverage because it's not actually being covered. There's
a separate ticket for removing that entirely.
i used this script, a little clunky but it got the job done
```bash
for file in `find . -type f -print | grep '\.go'`; do
sed '1,/^\/\/ limitations under the License.$/d' $file > $file.tmp;
result=`cat $file.tmp`
if [[ result != "" ]]; then
gofmt $file.tmp &> /dev/null;
if [[ $? == 0 ]]; then
mv $file.tmp $file && gofmt -w $file;
else
rm $file.tmp;
fi
else
rm $file.tmp;
fi
done
```
also adds a "noSleep" option to the server command to avoid the 5
second sleep we introduced on startup for non-coordinator cluster
nodes. The sleep doesn't seem to be needed in the tests and makes them
much slower.
gossip now takes a single "MemberServer" which is implemented by server. Several
interfaces have been removed.
MemberServer contains ReceiveMessage which is a superset of the functionality of
ReceiveEvent, LocalStatus and HandleRemoteStatus are all that's left of
StatusHandler - ClusterStatus was not used and is gone. The Node() method is
actually a subset of LocalStatus() functionality. Maybe we should break up
localstatus or remove Node... not sure.
Remove BroadcastReceiver test which was a bit silly.
NodeEvent can now be unexported, and is.
since the gossip MemberSet has access to Server, it wasn't really necessary to
pass it a Node object when calling Open on it from Cluster. The end goal is to
have it be removed from Cluster entirely, and have it be Opened externally, and
this is a step toward that.
Exposing Node method on Server doesn't really expose any more than was already
there as the same info can be gotten from LocalStatus with a bit of type
casting. I figured adding the method was a little cleaner, and we could collapse
all the functionality when the dust has settled.
The Cluster.open method has been broken into two parts - one of which happens
earlier (at NewServer time), and the other will eventually just be "waiting to
make sure we've joined the cluster". Right now it's calling Memberset.Open, and
then waiting to make sure the cluster has been joined.
Implement prefect in Cluster so a node can start http listener in a
restricted mode.
Adjust tests; particularly start test.Holder in state Normal.
TODO:
- [ ] fix test TestMain_SendReceiveMessage
- [ ] add additional tests for `nodeState`
