This PR adds two features which will be useful for operators when ACLs are in use.
1. Tokens set in configuration files are now reloadable.
2. If `acl.enable_token_persistence` is set to `true` in the configuration, tokens set via the `v1/agent/token` endpoint are now persisted to disk and loaded when the agent starts (or during configuration reload)
Note that token persistence is opt-in so our users who do not want tokens on the local disk will see no change.
Some other secondary changes:
* Refactored a bunch of places where the replication token is retrieved from the token store. This token isn't just for replicating ACLs and now it is named accordingly.
* Allowed better paths in the `v1/agent/token/` API. Instead of paths like: `v1/agent/token/acl_replication_token` the path can now be just `v1/agent/token/replication`. The old paths remain to be valid.
* Added a couple new API functions to set tokens via the new paths. Deprecated the old ones and pointed to the new names. The names are also generally better and don't imply that what you are setting is for ACLs but rather are setting ACL tokens. There is a minor semantic difference there especially for the replication token as again, its no longer used only for ACL token/policy replication. The new functions will detect 404s and fallback to using the older token paths when talking to pre-1.4.3 agents.
* Docs updated to reflect the API additions and to show using the new endpoints.
* Updated the ACL CLI set-agent-tokens command to use the non-deprecated APIs.
Given a query like:
```
{
"Name": "tagged-connect-query",
"Service": {
"Service": "foo",
"Tags": ["tag"],
"Connect": true
}
}
```
And a Consul configuration like:
```
{
"services": [
"name": "foo",
"port": 8080,
"connect": { "sidecar_service": {} },
"tags": ["tag"]
]
}
```
If you executed the query it would always turn up with 0 results. This was because the sidecar service was being created without any tags. You could instead make your config look like:
```
{
"services": [
"name": "foo",
"port": 8080,
"connect": { "sidecar_service": {
"tags": ["tag"]
} },
"tags": ["tag"]
]
}
```
However that is a bit redundant for most cases. This PR ensures that the tags and service meta of the parent service get copied to the sidecar service. If there are any tags or service meta set in the sidecar service definition then this copying does not take place. After the changes, the query will now return the expected results.
A second change was made to prepared queries in this PR which is to allow filtering on ServiceMeta just like we allow for filtering on NodeMeta.
* Support rate limiting and concurrency limiting CSR requests on servers; handle CA rotations gracefully with jitter and backoff-on-rate-limit in client
* Add CSR rate limiting docs
* Fix config naming and add tests for new CA configs
* Add default weights when adding a service with no weights to local state to prevent constant AE re-sync.
This fix was contributed by @42wim in https://github.com/hashicorp/consul/pull/5096 but was merged against the wrong base. This adds it to master and adds a test to cover the behaviour.
* Fix tests that broke due to comparing internal state which now has default weights
This endpoint aggregates all checks related to <service id> on the agent
and return an appropriate http code + the string describing the worst
check.
This allows to cleanly expose service status to other component, hiding
complexity of multiple checks.
This is especially useful to use consul to feed a load balancer which
would delegate health checking to consul agent.
Exposing this endpoint on the agent is necessary to avoid a hit on
consul servers and avoid decreasing resiliency (this endpoint will work
even if there is no consul leader in the cluster).
* Update the ACL API docs
* Add a CreateTime to the anon token
Also require acl:read permissions at least to perform rule translation. Don’t want someone DoSing the system with an open endpoint that actually does a bit of work.
* Fix one place where I was referring to id instead of AccessorID
* Add godocs for the API package additions.
* Minor updates: removed some extra commas and updated the acl intro paragraph
* minor tweaks
* Updated the language to be clearer
* Updated the language to be clearer for policy page
* I was also confused by that! Your updates are much clearer.
Co-Authored-By: kaitlincarter-hc <43049322+kaitlincarter-hc@users.noreply.github.com>
* Sounds much better.
Co-Authored-By: kaitlincarter-hc <43049322+kaitlincarter-hc@users.noreply.github.com>
* Updated sidebar layout and deprecated warning
* A few API mods and unit tests.
* Update the unit tests to verify query/write metadata and to fix the rules endpoint tests.
* Make sure the full information for the replication status is in the api packge
* Implement CLI token cloning & special ID handling
* Update a couple CLI commands to take some alternative options.
* Document the CLI.
* Update the policy list and set-agent-token synopsis
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.
* agent/debug: add package for debugging, host info
* api: add v1/agent/host endpoint
* agent: add v1/agent/host endpoint
* command/debug: implementation of static capture
* command/debug: tests and only configured targets
* agent/debug: add basic test for host metrics
* command/debug: add methods for dynamic data capture
* api: add debug/pprof endpoints
* command/debug: add pprof
* command/debug: timing, wg, logs to disk
* vendor: add gopsutil/disk
* command/debug: add a usage section
* website: add docs for consul debug
* agent/host: require operator:read
* api/host: improve docs and no retry timing
* command/debug: fail on extra arguments
* command/debug: fixup file permissions to 0644
* command/debug: remove server flags
* command/debug: improve clarity of usage section
* api/debug: add Trace for profiling, fix profile
* command/debug: capture profile and trace at the same time
* command/debug: add index document
* command/debug: use "clusters" in place of members
* command/debug: remove address in output
* command/debug: improve comment on metrics sleep
* command/debug: clarify usage
* agent: always register pprof handlers and protect
This will allow us to avoid a restart of a target agent
for profiling by always registering the pprof handlers.
Given this is a potentially sensitive path, it is protected
with an operator:read ACL and enable debug being
set to true on the target agent. enable_debug still requires
a restart.
If ACLs are disabled, enable_debug is sufficient.
* command/debug: use trace.out instead of .prof
More in line with golang docs.
* agent: fix comment wording
* agent: wrap table driven tests in t.run()
* Support multiple tags for health and catalog api endpoints
Fixes#1781.
Adds a `ServiceTags` field to the ServiceSpecificRequest to support
multiple tags, updates the filter logic in the catalog store, and
propagates these change through to the health and catalog endpoints.
Note: Leaves `ServiceTag` in the struct, since it is being used as
part of the DNS lookup, which in turn uses the health check.
* Update the api package to support multiple tags
Includes additional tests.
* Update new tests to use the `require` library
* Update HealthConnect check after a bad merge
Play a trick with CLOEXEC to pass the envoy bootstrap configuration as
an open file descriptor to the exec'd envoy process. The file only
briefly touches disk before being unlinked.
We convince envoy to read from this open file descriptor by using the
/dev/fd/$FDNUMBER mechanism to read the open file descriptor as a file.
Because the filename no longer has an extension envoy's sniffing logic
falls back on JSON instead of YAML, so the bootstrap configuration must
be generated as JSON instead.
* Plumb xDS server and proxyxfg into the agent startup
* Add `consul connect envoy` command to allow running Envoy as a connect sidecar.
* Add test for help tabs; typos and style fixups from review
- A new endpoint `/v1/agent/service/:service_id` which is a generic way to look up the service for a single instance. The primary value here is that it:
- **supports hash-based blocking** and so;
- **replaces `/agent/connect/proxy/:proxy_id`** as the mechanism the built-in proxy uses to read its config.
- It's not proxy specific and so works for any service.
- It has a temporary shim to call through to the existing endpoint to preserve current managed proxy config defaulting behaviour until that is removed entirely (tested).
- The built-in proxy now uses the new endpoint exclusively for it's config
- The built-in proxy now has a `-sidecar-for` flag that allows the service ID of the _target_ service to be specified, on the condition that there is exactly one "sidecar" proxy (that is one that has `Proxy.DestinationServiceID` set) for the service registered.
- Several fixes for edge cases for SidecarService
- A fix for `Alias` checks - when running locally they didn't update their state until some external thing updated the target. If the target service has no checks registered as below, then the alias never made it past critical.
* Added new Config for SidecarService in ServiceDefinitions.
* WIP: all the code needed for SidecarService is written... none of it is tested other than config :). Need API updates too.
* Test coverage for the new sidecarServiceFromNodeService method.
* Test API registratrion with SidecarService
* Recursive Key Translation 🤦
* Add tests for nested sidecar defintion arrays to ensure they are translated correctly
* Use dedicated internal state rather than Service Meta for tracking sidecars for deregistration.
Add tests for deregistration.
* API struct for agent register. No other endpoint should be affected yet.
* Additional test cases to cover updates to API registrations
* Refactor Service Definition ProxyDestination.
This includes:
- Refactoring all internal structs used
- Updated tests for both deprecated and new input for:
- Agent Services endpoint response
- Agent Service endpoint response
- Agent Register endpoint
- Unmanaged deprecated field
- Unmanaged new fields
- Managed deprecated upstreams
- Managed new
- Catalog Register
- Unmanaged deprecated field
- Unmanaged new fields
- Managed deprecated upstreams
- Managed new
- Catalog Services endpoint response
- Catalog Node endpoint response
- Catalog Service endpoint response
- Updated API tests for all of the above too (both deprecated and new forms of register)
TODO:
- config package changes for on-disk service definitions
- proxy config endpoint
- built-in proxy support for new fields
* Agent proxy config endpoint updated with upstreams
* Config file changes for upstreams.
* Add upstream opaque config and update all tests to ensure it works everywhere.
* Built in proxy working with new Upstreams config
* Command fixes and deprecations
* Fix key translation, upstream type defaults and a spate of other subtele bugs found with ned to end test scripts...
TODO: tests still failing on one case that needs a fix. I think it's key translation for upstreams nested in Managed proxy struct.
* Fix translated keys in API registration.
≈
* Fixes from docs
- omit some empty undocumented fields in API
- Bring back ServiceProxyDestination in Catalog responses to not break backwards compat - this was removed assuming it was only used internally.
* Documentation updates for Upstreams in service definition
* Fixes for tests broken by many refactors.
* Enable travis on f-connect branch in this branch too.
* Add consistent Deprecation comments to ProxyDestination uses
* Update version number on deprecation notices, and correct upstream datacenter field with explanation in docs
* Add cache types for catalog/services and health/services and basic test that caching works
* Support non-blocking cache types with Cache-Control semantics.
* Update API docs to include caching info for every endpoint.
* Comment updates per PR feedback.
* Add note on caching to the 10,000 foot view on the architecture page to make the new data path more clear.
* Document prepared query staleness quirk and force all background requests to AllowStale so we can spread service discovery load across servers.
* Add function to wait for serfHealth in api tests
* Disable connect when creating semaphore test clients
* Wait for serfHealth when creating sessions in their tests
* Add helper functions to create lock/semaphore sessions without checks
* Log passing tests to prevent timeout in Travis due to lack of output
* Implementation of Weights Data structures
Adding this datastructure will allow us to resolve the
issues #1088 and #4198
This new structure defaults to values:
```
{ Passing: 1, Warning: 0 }
```
Which means, use weight of 0 for a Service in Warning State
while use Weight 1 for a Healthy Service.
Thus it remains compatible with previous Consul versions.
* Implemented weights for DNS SRV Records
* DNS properly support agents with weight support while server does not (backwards compatibility)
* Use Warning value of Weights of 1 by default
When using DNS interface with only_passing = false, all nodes
with non-Critical healthcheck used to have a weight value of 1.
While having weight.Warning = 0 as default value, this is probably
a bad idea as it breaks ascending compatibility.
Thus, we put a default value of 1 to be consistent with existing behaviour.
* Added documentation for new weight field in service description
* Better documentation about weights as suggested by @banks
* Return weight = 1 for unknown Check states as suggested by @banks
* Fixed typo (of -> or) in error message as requested by @mkeeler
* Fixed unstable unit test TestRetryJoin
* Fixed unstable tests
* Fixed wrong Fatalf format in `testrpc/wait.go`
* Added notes regarding DNS SRV lookup limitations regarding number of instances
* Documentation fixes and clarification regarding SRV records with weights as requested by @banks
* Rephrase docs
- Improve resilience of testrpc.WaitForLeader()
- Add additionall retry to CI
- Increase "go test" timeout to 8m
- Add wait for cluster leader to several tests in the agent package
- Add retry to some tests in the api and command packages
* Copy-and-paste Go client example
Includes Go source that runs without modification, as well as simple
instructions for compiling, running, and viewing the output in the
Consul UI.
* Remove unnecessary flags from development server example
This is a bare minimum Go example needed to store keys and values in
Consul. The `-ui` and `-server` flags aren't needed when running with
`-dev`.
* Fix theoretical cache collision bug if/when we use more cache types with same result type
* Generalized fix for blocking query handling when state store methods return zero index
* Refactor test retry to only affect CI
* Undo make file merge
* Add hint to error message returned to end-user requests if Connect is not enabled when they try to request cert
* Explicit error for Roots endpoint if connect is disabled
* Fix tests that were asserting old behaviour
Few other fixes in here just to get a clean run locally - they are all also fixed in other PRs but shouldn't conflict.
This should be robust to timing between goroutines now.
There are also a lot of small bug fixes found when testing lots of things end-to-end for the first time and some cleanup now it's integrated with real CA code.
- Includes some bug fixes for previous `api` work and `agent` that weren't tested
- Needed somewhat pervasive changes to support hash based blocking - some TODOs left in our watch toolchain that will explicitly fail on hash-based watches.
- Integration into `connect` is partially done here but still WIP
* Refactors the HTTP listen path to create servers in the same spot.
* Adds HTTP/2 support to Consul's HTTPS server.
* Vendors Go HTTP/2 library and associated deps.
* Updates the API client to support the current `ScriptArgs` parameter
for checks.
* Updates docs for checks to explain the `ScriptArgs` parameter issue.
* Adds mappings for "args" and "script-args" to give th API parity
with config.
* Adds checks on return codes.
* Removes debug logging that shows empty when args are used.
* retry locks on network errors
When communicating with a local agent and watching a lock, a dropped
connection between the agent and server will show up as a server error
and immediately be retried. However if the client is connected to a
remote server, a dropped connection immediately aborts the lock.
* Updates comment about it being unsafe for writes.
* config: provide stable config for /v1/agent/self (#3530)
This patch adds a stable subset of the previous Config struct to the
agent/self response. The actual runtime configuration is moved into
DebugConfig and will be documented to change.
Fixes#3530
* config: fix tests
* doc: update api documentation for /v1/agent/self
* vendor: add github.com/sergi/go-diff/diffmatchpatch for diff'ing test output
* config: refactor Sanitize to recursively clean runtime config and format complex fields
* Removes an extra int cast.
* Adds a top-level check test case for sanitization.
* Changes default Raft protocol to 3.
* Changes numPeers() to report only voters.
This should have been there before, but it's more obvious that this
is incorrect now that we default the Raft protocol to 3, which puts
new servers in a read-only state while Autopilot waits for them to
become healthy.
* Fixes TestLeader_RollRaftServer.
* Fixes TestOperator_RaftRemovePeerByAddress.
* Fixes TestServer_*.
Relaxed the check for a given number of voter peers and instead do
a thorough check that all servers see each other in their Raft
configurations.
* Fixes TestACL_*.
These now just check for Raft replication to be set up, and don't
care about the number of voter peers.
* Fixes TestOperator_Raft_ListPeers.
* Fixes TestAutopilot_CleanupDeadServerPeriodic.
* Fixes TestCatalog_ListNodes_ConsistentRead_Fail.
* Fixes TestLeader_ChangeServerID and adjusts the conn pool to throw away
sockets when it sees io.EOF.
* Changes version to 1.0.0 in the options doc.
* Makes metrics test more deterministic with autopilot metrics possible.
* new config parser for agent
This patch implements a new config parser for the consul agent which
makes the following changes to the previous implementation:
* add HCL support
* all configuration fragments in tests and for default config are
expressed as HCL fragments
* HCL fragments can be provided on the command line so that they
can eventually replace the command line flags.
* HCL/JSON fragments are parsed into a temporary Config structure
which can be merged using reflection (all values are pointers).
The existing merge logic of overwrite for values and append
for slices has been preserved.
* A single builder process generates a typed runtime configuration
for the agent.
The new implementation is more strict and fails in the builder process
if no valid runtime configuration can be generated. Therefore,
additional validations in other parts of the code should be removed.
The builder also pre-computes all required network addresses so that no
address/port magic should be required where the configuration is used
and should therefore be removed.
* Upgrade github.com/hashicorp/hcl to support int64
* improve error messages
* fix directory permission test
* Fix rtt test
* Fix ForceLeave test
* Skip performance test for now until we know what to do
* Update github.com/hashicorp/memberlist to update log prefix
* Make memberlist use the default logger
* improve config error handling
* do not fail on non-existing data-dir
* experiment with non-uniform timeouts to get a handle on stalled leader elections
* Run tests for packages separately to eliminate the spurious port conflicts
* refactor private address detection and unify approach for ipv4 and ipv6.
Fixes#2825
* do not allow unix sockets for DNS
* improve bind and advertise addr error handling
* go through builder using test coverage
* minimal update to the docs
* more coverage tests fixed
* more tests
* fix makefile
* cleanup
* fix port conflicts with external port server 'porter'
* stop test server on error
* do not run api test that change global ENV concurrently with the other tests
* Run remaining api tests concurrently
* no need for retry with the port number service
* monkey patch race condition in go-sockaddr until we understand why that fails
* monkey patch hcl decoder race condidtion until we understand why that fails
* monkey patch spurious errors in strings.EqualFold from here
* add test for hcl decoder race condition. Run with go test -parallel 128
* Increase timeout again
* cleanup
* don't log port allocations by default
* use base command arg parsing to format help output properly
* handle -dc deprecation case in Build
* switch autopilot.max_trailing_logs to int
* remove duplicate test case
* remove unused methods
* remove comments about flag/config value inconsistencies
* switch got and want around since the error message was misleading.
* Removes a stray debug log.
* Removes a stray newline in imports.
* Fixes TestACL_Version8.
* Runs go fmt.
* Adds a default case for unknown address types.
* Reoders and reformats some imports.
* Adds some comments and fixes typos.
* Reorders imports.
* add unix socket support for dns later
* drop all deprecated flags and arguments
* fix wrong field name
* remove stray node-id file
* drop unnecessary patch section in test
* drop duplicate test
* add test for LeaveOnTerm and SkipLeaveOnInt in client mode
* drop "bla" and add clarifying comment for the test
* split up tests to support enterprise/non-enterprise tests
* drop raft multiplier and derive values during build phase
* sanitize runtime config reflectively and add test
* detect invalid config fields
* fix tests with invalid config fields
* use different values for wan sanitiziation test
* drop recursor in favor of recursors
* allow dns_config.udp_answer_limit to be zero
* make sure tests run on machines with multiple ips
* Fix failing tests in a few more places by providing a bind address in the test
* Gets rid of skipped TestAgent_CheckPerformanceSettings and adds case for builder.
* Add porter to server_test.go to make tests there less flaky
* go fmt
Cancellation channels are often derived from a Context, which
returns a directional `<-chan struct{}` from Done(). In order to use
this with parts of of the consul API, one is required to create a new
channel and dispatch a separate goroutine to watch for context
cancellation and close the new channel.
Changing the signature for the methods that take cancellation channels
will allow easier integration with existing uses of Context. Since the
cancellation pattern only reads from these channels, there should be no
backwards incompatibility with existing codebases, and most of the
methods already accept only the correct type.
This creates a simplified helper for temporary directories and files.
All path names are prefixed with the name of the current test.
All files and directories are stored either in /tmp/consul-test
or /tmp if the former could not be created.
Using the system temp dir breaks some tests on macOS where the unix
socket path becomes too long.
Refactor tests that use testutil.WaitForResult to use retry.
Since this requires refactoring the test functions in general this patch
also shows the use of the github.com/pascaldekloe/goe/verify library
which provides a good mechanism for comparing nested data structures.
Instead of just converting the tests from testutil.WaitForResult to
retry the tests that performing a nested comparison of data structures
are converted to the verify library at the same time.
This patch stores the datacenter of a node in memdb
and exposes it via the API in all places where a Node
structure is returned.
* /catalog/nodes
* /catalog/node/:node
* /catalog/service/:service
* /health/service/:service
* /query/:uuid/execute
This adds two goroutines to perform autopilot tasks on the leader - one
to monitor the health of servers and another to periodically clean up
dead servers with a limit on removal count. Also adds a new http endpoint,
`/v1/operator/autopilot/health`, for querying this information through an
operator RPC endpoint.
Given a list of HealthChecks, this determines the "best" status for the
collective group. This is useful for nodes and services, which may have
multiple checks associated with them.
* Updates Raft library to get new snapshot/restore API.
* Basic backup and restore working, but need some cleanup.
* Breaks out a snapshot module and adds a SHA256 integrity check.
* Adds snapshot ACL and fills in some missing comments.
* Require a consistent read for snapshots.
* Make sure snapshot works if ACLs aren't enabled.
* Adds a bit of package documentation.
* Returns an empty response from restore to avoid EOF errors.
* Adds API client support for snapshots.
* Makes internal file names match on-disk file snapshots.
* Adds DC and token coverage for snapshot API test.
* Adds missing documentation.
* Adds a unit test for the snapshot client endpoint.
* Moves the connection pool out of the client for easier testing.
* Fixes an incidental issue in the prepared query unit test.
I realized I had two servers in bootstrap mode so this wasn't a good setup.
* Adds a half close to the TCP stream and fixes panic on error.
* Adds client and endpoint tests for snapshots.
* Moves the pool back into the snapshot RPC client.
* Adds a TLS test and fixes half-closes for TLS connections.
* Tweaks some comments.
* Adds a low-level snapshot test.
This is independent of Consul so we can pull this out into a library
later if we want to.
* Cleans up snapshot and archive and completes archive tests.
* Sends a clear error for snapshot operations in dev mode.
Snapshots require the Raft snapshots to be readable, which isn't supported
in dev mode. Send a clear error instead of a deep-down Raft one.
* Adds docs for the snapshot endpoint.
* Adds a stale mode and index feedback for snapshot saves.
This gives folks a way to extract data even if the cluster has no
leader.
* Changes the internal format of a snapshot from zip to tgz.
* Pulls in Raft fix to cancel inflight before a restore.
* Pulls in new Raft restore interface.
* Adds metadata to snapshot saves and a verify function.
* Adds basic save and restore snapshot CLI commands.
* Gets rid of tarball extensions and adds restore message.
* Fixes an incidental bad link in the KV docs.
* Adds documentation for the snapshot CLI commands.
* Scuttle any request body when a snapshot is saved.
* Fixes archive unit test error message check.
* Allows for nil output writers in snapshot RPC handlers.
* Renames hash list Decode to DecodeAndVerify.
* Closes the client connection for snapshot ops.
* Lowers timeout for restore ops.
* Updates Raft vendor to get new Restore signature and integrates with Consul.
* Bounces the leader's internal state when we do a restore.
This isn't needed/used yet, but it's a good hook to get in there so we
can add more atomic operations in the future. The Go API hides this detail
so that feels like a KV-specific API. The implications on the REST API are
pretty minimal.
Previously, it would try once "up to" the timeout, but in practice it would
just fall through. This modifies the behavior to block until the timeout has
been reached.
Two of the changes are in tests; the one of consequence is in the API.
As explained in #1308 this can cause conflicts with downstream programs.
Fixes#1308.
Adds the ability to simply check whether a TCP socket accepts
connections to determine if it is healthy. This is a light-weight -
though less comprehensive than scripting - method of checking network
service health.
The check parameter `tcp` should be set to the `address:port`
combination for the service to be tested. Supports both IPv6 and IPv4,
in the case of a hostname that resolves to both, connections will be
attempted via both protocol versions, with the first successful
connection returning a successful check result.
Example check:
```json
{
"check": {
"id": "ssh",
"name": "SSH (TCP)",
"tcp": "example.com:22",
"interval": "10s"
}
}
```
This status must be one of the valid check statuses: 'passing', 'warning', 'critical', 'unknown'.
If the status field is not present or the empty string, the default of 'critical' is used.
R.B. Boyer