acl: reduce complexity of token resolution process with alternative singleflighting
Switches acl resolution to use golang.org/x/sync/singleflight. For the
identity/legacy lookups this is a drop-in replacement with the same
overall approach to request coalescing.
For policies this is technically a change in behavior, but when
considered holistically is approximately performance neutral (with the
benefit of less code).
There are two goals with this blob of code (speaking specifically of
policy resolution here):
1) Minimize cross-DC requests.
2) Minimize client-to-server LAN requests.
The previous iteration of this code was optimizing for the case of many
possibly different tokens being resolved concurrently that have a
significant overlap in linked policies such that deduplication would be
worth the complexity. While this is laudable there are some things to
consider that can help to adjust expectations:
1) For v1.4+ policies are always replicated, and once a single policy
shows up in a secondary DC the replicated data is considered
authoritative for requests made in that DC. This means that our
earlier concerns about minimizing cross-DC requests are irrelevant
because there will be no cross-DC policy reads that occur.
2) For Server nodes the in-memory ACL policy cache is capped at zero,
meaning it has no caching. Only Client nodes run with a cache. This
means that instead of having an entire DC's worth of tokens (what a
Server might see) that can have policy resolutions coalesced these
nodes will only ever be seeing node-local token resolutions. In a
reasonable worst-case scenario where a scheduler like Kubernetes has
"filled" a node with Connect services, even that will only schedule
~100 connect services per node. If every service has a unique token
there will only be 100 tokens to coalesce and even then those requests
have to occur concurrently AND be hitting an empty consul cache.
Instead of seeing a great coalescing opportunity for cutting down on
redundant Policy resolutions, in practice it's far more likely given
node densities that you'd see requests for the same token concurrently
than you would for two tokens sharing a policy concurrently (to a degree
that would warrant the overhead of the current variation of
singleflighting.
Given that, this patch switches the Policy resolution process to only
singleflight by requesting token (but keeps the cache as by-policy).
* Fix 2 remote ACL policy resolution issues
1 - Use the right method to fire async not found errors when the ACL.PolicyResolve RPC returns that error. This was previously accidentally firing a token result instead of a policy result which would have effectively done nothing (unless there happened to be a token with a secret id == the policy id being resolved.
2. When concurrent policy resolution is being done we single flight the requests. The bug before was that for the policy resolution that was going to piggy back on anothers RPC results it wasn’t waiting long enough for the results to come back due to looping with the wrong variable.
* Fix a handful of other edge case ACL scenarios
The main issue was that token specific issues (not able to access a particular policy or the token being deleted after initial fetching) were poisoning the policy cache.
A second issue was that for concurrent token resolutions, the first resolution to get started would go fetch all the policies. If before the policies were retrieved a second resolution request came in, the new request would register watchers for those policies but then never block waiting for them to complete. This resulted in using the default policy when it shouldn't have.
* Add leader token upgrade test and fix various ACL enablement bugs
* Update the leader ACL initialization tests.
* Add a StateStore ACL tests for ACLTokenSet and ACLTokenGetBy* functions
* Advertise the agents acl support status with the agent/self endpoint.
* Make batch token upsert CAS’able to prevent consistency issues with token auto-upgrade
* Finish up the ACL state store token tests
* Finish the ACL state store unit tests
Also rename some things to make them more consistent.
* Do as much ACL replication testing as I can.
This PR is almost a complete rewrite of the ACL system within Consul. It brings the features more in line with other HashiCorp products. Obviously there is quite a bit left to do here but most of it is related docs, testing and finishing the last few commands in the CLI. I will update the PR description and check off the todos as I finish them over the next few days/week.
Description
At a high level this PR is mainly to split ACL tokens from Policies and to split the concepts of Authorization from Identities. A lot of this PR is mostly just to support CRUD operations on ACLTokens and ACLPolicies. These in and of themselves are not particularly interesting. The bigger conceptual changes are in how tokens get resolved, how backwards compatibility is handled and the separation of policy from identity which could lead the way to allowing for alternative identity providers.
On the surface and with a new cluster the ACL system will look very similar to that of Nomads. Both have tokens and policies. Both have local tokens. The ACL management APIs for both are very similar. I even ripped off Nomad's ACL bootstrap resetting procedure. There are a few key differences though.
Nomad requires token and policy replication where Consul only requires policy replication with token replication being opt-in. In Consul local tokens only work with token replication being enabled though.
All policies in Nomad are globally applicable. In Consul all policies are stored and replicated globally but can be scoped to a subset of the datacenters. This allows for more granular access management.
Unlike Nomad, Consul has legacy baggage in the form of the original ACL system. The ramifications of this are:
A server running the new system must still support other clients using the legacy system.
A client running the new system must be able to use the legacy RPCs when the servers in its datacenter are running the legacy system.
The primary ACL DC's servers running in legacy mode needs to be a gate that keeps everything else in the entire multi-DC cluster running in legacy mode.
So not only does this PR implement the new ACL system but has a legacy mode built in for when the cluster isn't ready for new ACLs. Also detecting that new ACLs can be used is automatic and requires no configuration on the part of administrators. This process is detailed more in the "Transitioning from Legacy to New ACL Mode" section below.
It will allow the following:
* when connectivity is limited (saturated linnks between DCs), only one
single request to refresh an ACL will be sent to ACL master DC instead
of statcking ACL refresh queries
* when extend-cache is used for ACL, do not wait for result, but refresh
the ACL asynchronously, so no delay is not impacting slave DC
* When extend-cache is not used, keep the existing blocking mechanism,
but only send a single refresh request.
This will fix https://github.com/hashicorp/consul/issues/3524
The error handling of the ACL code relies on the presence of certain
magic error messages. Since the error values are sent via RPC between
older and newer consul agents we cannot just replace the magic values
with typed errors and switch to type checks since this would break
compatibility with older clients.
Therefore, this patch moves all magic ACL error messages into the acl
package and provides default error values and helper functions which
determine the type of error.
* Moves magic check and service constants into shared structs package.
* Removes the "consul" service from local state.
Since this service is added by the leader, it doesn't really make sense to
also keep it in local state (which requires special ACLs to configure), and
requires a bunch of special cases in the local state logic. This requires
fewer special cases and makes ACL bootstrapping cleaner.
* Makes coordinate update ACL log message a warning, similar to other AE warnings.
* Adds much more detailed examples for bootstrapping ACLs.
This can hopefully replace https://gist.github.com/slackpad/d89ce0e1cc0802c3c4f2d84932fa3234.
