pkg/trace/api: add /info discovery endpoint

[gbbr]

Example response from http://localhost:8126/info:

{
	"version": "0.99.0",
	"git_commit": "fab047e10",
	"build_date": "2020-12-04 15:57:06.74187 +0200 EET m=+0.029001792",
	"endpoints": [
		"/v0.3/traces",
		"/v0.3/services",
		"/v0.4/traces",
		"/v0.4/services",
		"/v0.5/traces",
		"/v0.5/stats",
		"/profiling/v1/input"
	],
	"feature_flags": [
		"feature_flag"
	],
	"config": {
		"default_env": "prod",
		"bucket_interval": 1000000000,
		"extra_aggregators": [
			"agg:val"
		],
		"extra_sample_rate": 2.4,
		"target_tps": 11,
		"max_eps": 12,
		"receiver_port": 8111,
		"receiver_socket": "/sock/path",
		"connection_limit": 12,
		"receiver_timeout": 100,
		"max_request_bytes": 123,
		"statsd_port": 123,
		"max_memory": 1000000,
		"max_cpu": 12345,
		"analyzed_rate_by_service_legacy": {
			"X": 1.2
		},
		"analyzed_spans_by_service": {
			"X": {
				"Y": 2.4
			}
		},
		"obfuscation": {
			"elastic_search": true,
			"mongo": true,
			"sql_exec_plan": true,
			"sql_exec_plan_normalize": true,
			"http": {
				"remove_query_string": true,
				"remove_path_digits": true
			},
			"remove_stack_traces": false,
			"redis": true,
			"memcached": false
		}
	}
}

[richardstartin]

Hi @gbbr

What do values like those below mean? It looks to me like a feature flag hasn't been set. The client wouldn't expect these to be null but booleans. These would parse as false in some languages but I believe they are actually set by default in the trace agent.

"Obfuscation": null,
"ReplaceTags": null

This one looks like an actually nullable value, rather than the consequence of an unset feature flag, and I'd argue complete absence is a better policy in this case.

"ProxyURL": null

[gbbr]

@richardstartin nothing that is in the Config is a feature flag. A "feature flag" is simply an experimental option that may be enabled or not (and will eventually be removed in subsequent versions) currently showing up in FeatureFlags section. I just want to clear that off so that there's no miscommunication moving forward.

Obfuscation and ReplaceTags are both objects, not booleans. I have made a new commit to leave this out from the response when they are null. They specify the configuration for the obfuscator, basically the contents of that section in the datadog.yaml file (see this link). As for the tag replacer, see this link. Most of what's in the Config key is from that file...

[gbbr]

If it helps, here's a fully populated example object from the tests:

datadog-agent/pkg/trace/api/api_test.go

Lines 687 to 843 in c16442c

	"Version": "0.99.0",
	"GitCommit": "fab047e10",
	"BuildDate": "2020-12-04 15:57:06.74187 +0200 EET m=+0.029001792",
	"Endpoints": [
	"/v0.3/traces",
	"/v0.3/services",
	"/v0.4/traces",
	"/v0.4/services",
	"/v0.5/traces",
	"/v0.5/stats",
	"/profiling/v1/input"
	],
	"FeatureFlags": [
	"feature_flag"
	],
	"Config": {
	"Enabled": true,
	"Hostname": "test.host.name",
	"DefaultEnv": "prod",
	"ConfigPath": "/path/to/config",
	"Endpoints": [
	{
	"Host": "https://target-intake.datadoghq.com",
	"NoProxy": true
	}
	],
	"BucketInterval": 1000000000,
	"ExtraAggregators": [
	"agg:val"
	],
	"ExtraSampleRate": 2.4,
	"TargetTPS": 11,
	"MaxEPS": 12,
	"ReceiverHost": "localhost",
	"ReceiverPort": 8111,
	"ReceiverSocket": "/sock/path",
	"ConnectionLimit": 12,
	"ReceiverTimeout": 100,
	"MaxRequestBytes": 123,
	"StatsWriter": {
	"ConnectionLimit": 20,
	"QueueSize": 12,
	"FlushPeriodSeconds": 14.4
	},
	"TraceWriter": {
	"ConnectionLimit": 21,
	"QueueSize": 13,
	"FlushPeriodSeconds": 15.4
	},
	"ConnectionResetInterval": 0,
	"StatsdHost": "stastd.localhost",
	"StatsdPort": 123,
	"LogLevel": "WARN",
	"LogFilePath": "/path/to/logfile",
	"LogThrottling": false,
	"MaxMemory": 1000000,
	"MaxCPU": 12345,
	"WatchdogInterval": 60000000000,
	"ProxyURL": {
	"Scheme": "http",
	"Opaque": "",
	"User": null,
	"Host": "localhost:8888",
	"Path": "/proxy",
	"RawPath": "",
	"ForceQuery": false,
	"RawQuery": "",
	"Fragment": "",
	"RawFragment": ""
	},
	"SkipSSLValidation": false,
	"Ignore": {
	"K": [
	"1",
	"2"
	]
	},
	"ReplaceTags": [
	{
	"Name": "a",
	"Pattern": "*",
	"Re": null,
	"Repl": "b"
	}
	],
	"AnalyzedRateByServiceLegacy": {
	"X": 1.2
	},
	"AnalyzedSpansByService": {
	"X": {
	"Y": 2.4
	}
	},
	"DDAgentBin": "/path/to/core/agent",
	"Obfuscation": {
	"ES": {
	"Enabled": true,
	"KeepValues": [
	"a",
	"b",
	"c"
	],
	"ObfuscateSQLValues": [
	"x",
	"y"
	]
	},
	"Mongo": {
	"Enabled": true,
	"KeepValues": [
	"a",
	"b",
	"c"
	],
	"ObfuscateSQLValues": [
	"x",
	"y"
	]
	},
	"SQLExecPlan": {
	"Enabled": true,
	"KeepValues": [
	"a",
	"b",
	"c"
	],
	"ObfuscateSQLValues": [
	"x",
	"y"
	]
	},
	"SQLExecPlanNormalize": {
	"Enabled": true,
	"KeepValues": [
	"a",
	"b",
	"c"
	],
	"ObfuscateSQLValues": [
	"x",
	"y"
	]
	},
	"HTTP": {
	"RemoveQueryString": true,
	"RemovePathDigits": true
	},
	"RemoveStackTraces": false,
	"Redis": {
	"Enabled": true
	},
	"Memcached": {
	"Enabled": false
	}
	}
	}
	}` {

[gbbr]

Removed ProxyURL which is probably not interesting at all to a tracer... The rest we can leave for debugging...

[gbbr]

@dougqh @richardstartin I took all of your feedback, and made the Go code uglier in order to get prettier JSON. I also manually selected which config options should show up, and removed any which seemed like they might contain sensitive information or be irrelevant to the user tracer. Furthermore, I made the obfuscation configurations as booleans as requested.

Please check the updated PR description and let me know your thoughts.

[richardstartin]

👍🏻

[raphaelgavache]

nice, I didn't know that there is field ordering on the JSON marshal. I would have expected maps to be flaky due to go random iterations

[gbbr]

Maps can't be flaky in ordering when they have only one element 🤷‍♂️ 😄 I didn't even notice.