This is like a Möbius strip of code due to the fact that low-level components (serf/memberlist) are connected to high-level components (the catalog and mesh-gateways) in a twisty maze of references which make it hard to dive into. With that in mind here's a high level summary of what you'll find in the patch:
There are several distinct chunks of code that are affected:
* new flags and config options for the server
* retry join WAN is slightly different
* retry join code is shared to discover primary mesh gateways from secondary datacenters
* because retry join logic runs in the *agent* and the results of that
operation for primary mesh gateways are needed in the *server* there are
some methods like `RefreshPrimaryGatewayFallbackAddresses` that must occur
at multiple layers of abstraction just to pass the data down to the right
layer.
* new cache type `FederationStateListMeshGatewaysName` for use in `proxycfg/xds` layers
* the function signature for RPC dialing picked up a new required field (the
node name of the destination)
* several new RPCs for manipulating a FederationState object:
`FederationState:{Apply,Get,List,ListMeshGateways}`
* 3 read-only internal APIs for debugging use to invoke those RPCs from curl
* raft and fsm changes to persist these FederationStates
* replication for FederationStates as they are canonically stored in the
Primary and replicated to the Secondaries.
* a special derivative of anti-entropy that runs in secondaries to snapshot
their local mesh gateway `CheckServiceNodes` and sync them into their upstream
FederationState in the primary (this works in conjunction with the
replication to distribute addresses for all mesh gateways in all DCs to all
other DCs)
* a "gateway locator" convenience object to make use of this data to choose
the addresses of gateways to use for any given RPC or gossip operation to a
remote DC. This gets data from the "retry join" logic in the agent and also
directly calls into the FSM.
* RPC (`:8300`) on the server sniffs the first byte of a new connection to
determine if it's actually doing native TLS. If so it checks the ALPN header
for protocol determination (just like how the existing system uses the
type-byte marker).
* 2 new kinds of protocols are exclusively decoded via this native TLS
mechanism: one for ferrying "packet" operations (udp-like) from the gossip
layer and one for "stream" operations (tcp-like). The packet operations
re-use sockets (using length-prefixing) to cut down on TLS re-negotiation
overhead.
* the server instances specially wrap the `memberlist.NetTransport` when running
with gateway federation enabled (in a `wanfed.Transport`). The general gist is
that if it tries to dial a node in the SAME datacenter (deduced by looking
at the suffix of the node name) there is no change. If dialing a DIFFERENT
datacenter it is wrapped up in a TLS+ALPN blob and sent through some mesh
gateways to eventually end up in a server's :8300 port.
* a new flag when launching a mesh gateway via `consul connect envoy` to
indicate that the servers are to be exposed. This sets a special service
meta when registering the gateway into the catalog.
* `proxycfg/xds` notice this metadata blob to activate additional watches for
the FederationState objects as well as the location of all of the consul
servers in that datacenter.
* `xds:` if the extra metadata is in place additional clusters are defined in a
DC to bulk sink all traffic to another DC's gateways. For the current
datacenter we listen on a wildcard name (`server.<dc>.consul`) that load
balances all servers as well as one mini-cluster per node
(`<node>.server.<dc>.consul`)
* the `consul tls cert create` command got a new flag (`-node`) to help create
an additional SAN in certs that can be used with this flavor of federation.
* xDS Mesh Gateway Resolver Subset Fixes
The first fix was that clusters were being generated for every service resolver subset regardless of there being any service instances of the associated service in that dc. The previous logic didn’t care at all but now it will omit generating those clusters unless we also have service instances that should be proxied.
The second fix was to respect the DefaultSubset of a service resolver so that mesh-gateways would configure the endpoints of the unnamed subset cluster to only those endpoints matched by the default subsets filters.
* Refactor the gateway endpoint generation to be a little easier to read
Fixes: #5396
This PR adds a proxy configuration stanza called expose. These flags register
listeners in Connect sidecar proxies to allow requests to specific HTTP paths from outside of the node. This allows services to protect themselves by only
listening on the loopback interface, while still accepting traffic from non
Connect-enabled services.
Under expose there is a boolean checks flag that would automatically expose all
registered HTTP and gRPC check paths.
This stanza also accepts a paths list to expose individual paths. The primary
use case for this functionality would be to expose paths for third parties like
Prometheus or the kubelet.
Listeners for requests to exposed paths are be configured dynamically at run
time. Any time a proxy, or check can be registered, a listener can also be
created.
In this initial implementation requests to these paths are not
authenticated/encrypted.
Failover is pushed entirely down to the data plane by creating envoy
clusters and putting each successive destination in a different load
assignment priority band. For example this shows that normally requests
go to 1.2.3.4:8080 but when that fails they go to 6.7.8.9:8080:
- name: foo
load_assignment:
cluster_name: foo
policy:
overprovisioning_factor: 100000
endpoints:
- priority: 0
lb_endpoints:
- endpoint:
address:
socket_address:
address: 1.2.3.4
port_value: 8080
- priority: 1
lb_endpoints:
- endpoint:
address:
socket_address:
address: 6.7.8.9
port_value: 8080
Mesh gateways route requests based solely on the SNI header tacked onto
the TLS layer. Envoy currently only lets you configure the outbound SNI
header at the cluster layer.
If you try to failover through a mesh gateway you ideally would
configure the SNI value per endpoint, but that's not possible in envoy
today.
This PR introduces a simpler way around the problem for now:
1. We identify any target of failover that will use mesh gateway mode local or
remote and then further isolate any resolver node in the compiled discovery
chain that has a failover destination set to one of those targets.
2. For each of these resolvers we will perform a small measurement of
comparative healths of the endpoints that come back from the health API for the
set of primary target and serial failover targets. We walk the list of targets
in order and if any endpoint is healthy we return that target, otherwise we
move on to the next target.
3. The CDS and EDS endpoints both perform the measurements in (2) for the
affected resolver nodes.
4. For CDS this measurement selects which TLS SNI field to use for the cluster
(note the cluster is always going to be named for the primary target)
5. For EDS this measurement selects which set of endpoints will populate the
cluster. Priority tiered failover is ignored.
One of the big downsides to this approach to failover is that the failover
detection and correction is going to be controlled by consul rather than
deferring that entirely to the data plane as with the prior version. This also
means that we are bound to only failover using official health signals and
cannot make use of data plane signals like outlier detection to affect
failover.
In this specific scenario the lack of data plane signals is ok because the
effectiveness is already muted by the fact that the ultimate destination
endpoints will have their data plane signals scrambled when they pass through
the mesh gateway wrapper anyway so we're not losing much.
Another related fix is that we now use the endpoint health from the
underlying service, not the health of the gateway (regardless of
failover mode).
In addition to exposing compilation over the API cleaned up the structures that would be exchanged to be cleaner and easier to support and understand.
Also removed ability to configure the envoy OverprovisioningFactor.
* Proxy Config Manager
This component watches for local state changes on the agent and ensures that each service registered locally with Kind == connect-proxy has it's state being actively populated in the cache.
This serves two purposes:
1. For the built-in proxy, it ensures that the state needed to accept connections is available in RAM shortly after registration and likely before the proxy actually starts accepting traffic.
2. For (future - next PR) xDS server and other possible future proxies that require _push_ based config discovery, this provides a mechanism to subscribe and be notified about updates to a proxy instance's config including upstream service discovery results.
* Address review comments
* Better comments; Better delivery of latest snapshot for slow watchers; Embed Config
* Comment typos
* Add upstream Stringer for funsies
R.B. Boyer