consul-esm

README

Consul ESM (External Service Monitor)

This project provides a daemon to run alongside Consul in order to run health checks for external nodes and update the status of those health checks in the catalog. It can also manage updating the coordinates of these external nodes, if enabled. See Consul's External Services guide for some more information about external nodes.

In order for the ESM to detect external nodes and health checks, any external nodes must be registered directly with the catalog with "external-node": "true" set in the node metadata. Health checks can also be registered with a 'Definition' field which includes the details of running the check. For example:

$ curl --request PUT --data @node.json localhost:8500/v1/catalog/register

node.json:

{
  "Datacenter": "dc1",
  "ID": "40e4a748-2192-161a-0510-9bf59fe950b5",
  "Node": "foo",
  "Address": "192.168.0.1",
  "TaggedAddresses": {
    "lan": "192.168.0.1",
    "wan": "192.168.0.1"
  },
  "NodeMeta": {
    "external-node": "true",
    "external-probe": "true"
  },
  "Service": {
    "ID": "web1",
    "Service": "web",
    "Tags": [
      "v1"
    ],
    "Address": "127.0.0.1",
    "Port": 8000
  },
  "Checks": [{
    "Node": "foo",
    "CheckID": "service:web1",
    "Name": "Web HTTP check",
    "Notes": "",
    "Status": "passing",
    "ServiceID": "web1",
    "Definition": {
      "HTTP": "http://localhost:8000/health",
      "Interval": "10s",
      "Timeout": "5s"
    }
  },{
    "Node": "foo",
    "CheckID": "service:web2",
    "Name": "Web TCP check",
    "Notes": "",
    "Status": "passing",
    "ServiceID": "web1",
    "Definition": {
      "TCP": "localhost:8000",
      "Interval": "5s",
      "Timeout": "1s",
      "DeregisterCriticalServiceAfter": "30s"
     }
  }]
}

The external-probe field determines whether the ESM will do regular pings to the node and maintain an externalNodeHealth check for the node (similar to the serfHealth check used by Consul agents).

The ESM will perform a leader election by holding a lock in Consul, and the leader will then continually watch Consul for updates to the catalog and perform health checks defined on any external nodes it discovers. This allows externally registered services and checks to access the same features as if they were registered locally on Consul agents.

Command Line

To run the daemon, pass the -config-file or -config-dir flag, giving the location of a config file or a directory containing .json or .hcl files.

$ consul-esm -config-file=/path/to/config.hcl -config-dir /etc/consul-esm.d
Consul ESM running!
            Datacenter: "dc1"
               Service: "consul-esm"
            Leader Key: "consul-esm/lock"
Node Reconnect Timeout: "72h"

Log data will now stream in as it occurs:

2017/10/31 21:59:41 [INFO] Waiting to obtain leadership...
2017/10/31 21:59:41 [INFO] Obtained leadership
2017/10/31 21:59:42 [DEBUG] agent: Check 'foo/service:web1' is passing
2017/10/31 21:59:42 [DEBUG] agent: Check 'foo/service:web2' is passing

Configuration

Configuration files can be provided in either JSON or HashiCorp Configuration Language (HCL) format. For more information, please see the HCL specification. The following is an example HCL config file, with the default values filled in:

// The log level to use.
log_level = "INFO"

// Controls whether to enable logging to syslog.
enable_syslog = false

// The syslog facility to use, if enabled.
syslog_facility = ""

// The service name for this agent to use when registering itself with Consul.
consul_service = "consul-esm"

// The path of the leader key that this agent will try to acquire before
// stepping up as a leader for the local Consul cluster. Should be the same
// across all Consul ESM agents in the datacenter.
consul_leader_key = "consul-esm/lock"

// The node metadata values used for the ESM to qualify a node in the catalog
// as an "external node".
external_node_meta {
    instance_type = "c3.large"
}

// The length of time to wait before reaping an external node due to failed
// pings.
node_reconnect_timeout = "72h"

// The address of the local Consul agent. Can also be provided through the
// CONSUL_HTTP_ADDR environment variable.
http_addr = "localhost:8500"

// The ACL token to use when communicating with the local Consul agent. Can
// also be provided through the CONSUL_HTTP_TOKEN environment variable.
token = ""

// The Consul datacenter to use.
datacenter = "dc1"

// The CA file to use for talking to Consul over TLS. Can also be provided
// though the CONSUL_CACERT environment variable.
ca_file = ""

// The path to a directory of CA certs to use for talking to Consul over TLS.
// Can also be provided through the CONSUL_CAPATH environment variable.
ca_path = ""

// The client cert file to use for talking to Consul over TLS. Can also be
// provided through the CONSUL_CLIENT_CERT environment variable.
cert_file = ""

// The client key file to use for talking to Consul over TLS. Can also be
// provided through the CONSUL_CLIENT_KEY environment variable.
key_file = ""

// The server name to use as the SNI host when connecting to Consul via TLS.
// Can also be provided through the CONSUL_TLS_SERVER_NAME environment
// variable.
tls_server_name = ""

Building

The Makefile contains commands for testing and building the ESM:

To build for local development:

make dev

To run the test suite:

make test

To build for a specific platform:

make darwin/amd64
make linux/amd64
...

To build for all supported platforms:

make build