cueball is a node.js library for "playing pool" -- managing a pool of
connections to a multi-node service where nodes are listed in DNS.
It supports DNS SRV record style services, as well as the simpler kind with multiple A/AAAA records under the same name, correctly respecting record TTLs and making use of Additional sections where possible.
The library also includes an HTTP Agent which can be used with the regular
node http client stack, including libraries like restify which layer on
top of it. The Agent transparently creates pools for services as you make
requests to connect to them.
npm install cueball
Using the HttpsAgent:
const mod_cueball = require('cueball');
const mod_restify = require('restify-clients');
var client = mod_restify.createStringClient({
url: 'https://us-east.manta.joyent.com',
agent: new mod_cueball.HttpsAgent({
spares: 4, maximum: 10,
recovery: {
default: {
timeout: 2000,
retries: 5,
delay: 250,
maxDelay: 1000
}
}
})
});
client.get('/foobar/public', function (err, req, res, data) {
...
});
This will create a connection pool that aims to keep 4 spare connections at
all times, up to a maximum of 10 total connections, for
us-east.manta.joyent.com.
It will respect DNS TTLs and automatically rebalance the pool as IP addresses are added to or removed from DNS.
new mod_cueball.HttpAgent(options)new mod_cueball.HttpsAgent(options)Creates an HTTP(S) agent that can be used with the node http client API.
Parameters
options -- Object, with keys:
recovery -- Object, a recovery spec (see below)resolvers -- optional Array of String, either containing IP addresses to
use as nameservers, or a single string for Dynamic Resolver modelog -- optional Object, a bunyan-style logger to usespares -- optional Number, number of spares wanted in the pool per hostmaximum -- optional Number, maximum number of connections per hostinitialDomains -- optional Array of String, initial domains to create
connections to at startup (to pre-seed the Agent for quick user later)tcpKeepAliveInitialDelay -- optional Number, if supplied, enable TCP
level keep-alives with the given initial delay (in milliseconds)ping -- optional String, URL path to use for health checking. Connection
is considered still viable if this URL returns a non-5xx response code.pingInterval -- optional Number, interval between health check pingserrorOnEmpty -- optional BooleanStops the pools managed by this agent, calling cb (if given) once all have
stopped.
Once an Agent has been stopped, it can no longer accept any new requests, and
will throw an Error if asked to do so. Calling stop() more than once is
also an error and will throw.
Parameters
cb -- optional Function (err)new mod_cueball.ConnectionPool(options)Creates a new pool of connections. There are two ways of using a ConnectionPool. You can either provide your own resolver directly, or provide parameters with which to create the default, DNS-based resolver.
Parameters
options -- Object, with keys:
constructor -- Function(backend) -> object, must open a new connection
to the given backend and return itdomain -- String, name to look up to find backends.recovery -- Object, a recovery spec (see below)service -- optional String, name of SRV service (e.g. _http._tcp)defaultPort -- optional Number, port to use for plain A/AAAA recordsresolvers -- optional Array of String, either containing IP addresses to
use as nameservers, or a single string for Dynamic Resolver mode (default
uses system resolvers from /etc/resolv.conf)log -- optional Object, a bunyan-style logger to usespares -- optional Number, number of spares wanted in the pool per hostmaximum -- optional Number, maximum number of connections per hostmaxDNSConcurrency -- optional Number, max number of DNS queries to issue
at once (default 5)checkTimeout -- optional Number, milliseconds of idle time before
running checker on a connectionchecker -- optional Function(handle, connection), to be run on idle
connectionsresolver -- optional instance of an object meeting the Resolver interface
below. You would typically obtain this object by either creating your own
Resolver directly or using the resolverForIpOrDomain function.Do not confuse resolvers (the list of IP addresses for the DNS resolvers to
contact) with resolver (a custom object meeting the Resolver interface below).
If you want to use a custom resolver, then you must specify the resolver
property. In that case, the resolvers, maxDNSConcurrency, defaultPort,
and recovery options are ignored, and the domain and service properties
are used only for logging.
Otherwise, if want to use the default DNS-based resolver, do not specify the
resolver property. A resolver instance will be created based on the other
configuration properties.
ConnectionPool exposes the mooremachine FSM interface, with the following
state graph:
| (from failed)
.stop() v
+--------+ connect ok +-------+ +--------+
init --> |starting| +------------> |running| +---> |stopping|
+--------+ +-------+ +--------+
+ ^ + +
resolver | | | |
failed | | | |
OR | +------+ | | v
retries +----> |failed| +-----+ | +-------+
exhausted +------+ connect ok | |stopped|
+ ^ | +-------+
| | |
.stop()| +----------------+
| all retries exhausted
Pools begin their life in the "starting" state. Once they have successfully made one connection to any backend, they proceed to the "running" state. Otherwise, if their underlying Resolver enters the "failed" state, or they exhaust their retry policy attempting to connect to all their backends, they enter the "failed" state.
A "running" pool can then either be stopped by calling the .stop() method, at
which point it enters the "stopping" state and begins tearing down its
connections; or all of its connections become disconnected and it exhausts its
retry policy, in which case it enters the "failed" state.
Failed pools can re-enter the "running" state at any time if they make a
successful connection to a backend and their underlying Resolver is no longer
"failed". A "failed" pool can also have the .stop() method called, in which
case it proceeds much as from "running".
ConnectionPool#stop()Stops the connection pool and its Resolver, then destroys all connections.
ConnectionPool#claim([options, ]callback)Claims a connection from the pool ready for use.
Parameters
options -- optional Object, with keys:
timeout -- optional Number, timeout for request in ms
(default Infinity)errorOnEmpty -- optional Boolean, if true return error straight away
if the pool has no backends at all (i.e., nothing was found in DNS)callback -- Function(err[, handle, connection]), parameters:
err -- an Error object, if the request could not be fulfilled or timed
outhandle -- Object, handle to be used to release the connection back to
the pool when work is completeconnection -- Object, the actual connection (as returned by the
constructor given to new ConnectionPool())Returns a "waiter handle", which is an Object having a cancel() method. The
cancel() method may be called at any time up to when the callback is run, to
cancel the request to the pool and relinquish any queue positions held.
When a client is done with a connection, they must call handle.release() to
return it to the pool. All event handlers should be disconnected from the
connection prior to calling release().
If a client determines that a connection must be closed immediately (e.g. due
to a protocol error making it impossible to continue using it safely), it must
call the .close() method on the handle, not any .destroy() or similar
method on the connection itself.
Calling claim() on a Pool that is in the "stopping", "stopped" or "failed"
states will result in the callback being called with an error on the next run of
the event loop.
ConnectionPool#claimSync()Claims a connection from the pool, only if an idle one is immediately available. Otherwise, throws an Error. Always throws an Error if called on a Pool that is "stopping", "stopped" or "failed".
Returns an Object with keys:
handle -- Object, handle to be used to release the connectionconnection -- Object, actual connectionmod_cueball.Resolver interfaceAn interface for all "resolvers", objects which take in some kind of configuration (e.g. a DNS name) and track a list of "backends" for that name. A "backend" is an IP/port pair that describes an endpoint that can be connected to to reach a given service.
Resolver exposes the mooremachine FSM interface, with the following state
graph:
.start() error
+-------+ +--------+ +------+
init -> |stopped| +---> |starting| +---> |failed|
+---+---+ +---+----+ +------+
^ | +
| | ok |
| v |
+---+----+ +---+---+ |
|stopping| <--+ |running| <--------+
+--------+ +-------+ retry success
.stop()
Resolvers begin their life "stopped". When the user calls .start(), they
begin the process of resolving the name/configuration they were given into
backends.
If the initial attempt to resolve the name/configuration fails, the Resolver enters the "failed" state, but continues retrying. If it succeeds, or if any later retry succeeds, it moves to the "running" state. The reason why the "failed" state exists is so that commandline tools and other short-lived processes can make use of it to decide when to "give up" on a name resolution.
Once an attempt has succeeded, the Resolver will begin emitting added and
removed events (see below) describing the backends that it has found.
In the "running" state, the Resolver continues to monitor the source of its backends (e.g. in DNS by retrying once the TTL expires) and emitting these events when changes occur.
Finally, when the .stop() method is called, the Resolver transitions to
"stopping", stops monitoring and emitting events, and comes to rest in the
"stopped" state where it started.
Resolver#start()Starts the resolver's normal operation (by beginning the process of looking up the names given).
Resolver#stop()Stops the resolver. No further events will be emitted unless start() is
called again.
Resolver#getLastError()Returns the last error experienced by the Resolver. This is particularly useful when the Resolver is in the "failed" state, to produce a log message or user interface text.
Resolver#getState()Returns the current state of the Resolver as a string (see diagram above).
Inherited from mod_mooremachine.FSM.
Resolver#onState(state, cb)Registers an event handler to run when the Resolver enters the given state.
Inherited from mod_mooremachine.FSM.
Resolver->added(key, backend)Emitted when a new backend has been found.
Parameters
key -- String, a unique key for this backend (will be referenced by any
subsequent events about this backend)backend -- Object, with keys:
name -- String, the DNS name for this backendaddress -- String, an IPv4 or IPv6 addressport -- NumberResolver->removed(key)Emitted when an existing backend has been removed.
Parameters
key -- String, unique key for this backendnew mod_cueball.DNSResolver(options)Creates a Resolver that looks up a name in DNS. This Resolver prefers SRV records if they are available, and falls back to A/AAAA records if they cannot be found.
Parameters
options -- Object, with keys:
domain -- String, name to look up to find backendsrecovery -- Object, a recovery spec (see below)service -- optional String, name of SRV service (e.g. _http._tcp)defaultPort -- optional Number, port to use for plain A/AAAA recordsresolvers -- optional Array of String, either containing IP addresses to
use as nameservers, or a single string for Dynamic Resolver mode (default
uses system resolvers from /etc/resolv.conf)log -- optional Object, a bunyan-style logger to usemaxDNSConcurrency -- optional Number, max number of DNS queries to issue
at once (default 5)new mod_cueball.StaticIpResolver(options)Creates a new static IP resolver. This object matches the Resolver interface
above, but emits a fixed list of IP addresses when started. This list never
changes. This is intended for development environments and debugging tools,
where a user may have provided an explicit IP address rather than a DNS name to
contact. See also: resolverForIpOrDomain().
Parameters
options -- Object, with keys:
backends -- Array of objects, each having properties:
address -- String, an IP address to emit as a backendport -- Number, a port number for this backendThis object provides the same start() and stop() methods as the Resolver
class, as well as the same added and removed events.
resolverForIpOrDomain(options)Services that use DNS for service discovery would typically use a DNS-based resolver. But in development environments or with debugging tools, it's useful to be able to point a cueball-using program at an instance located at a specific IP address and port. That's what the Static IP resolver is for.
To make this easy for programs that want to support connecting to either hostnames or IP addresses, this function is provided to take configuration (expected to come from a user, via an environment variable, command-line option, or other configuration source), determine whether an IP address or DNS name was specified, and return either a DNS-based or static resolver. If the input appears to be neither a valid IPv4 nor IPv6 address nor DNS name, or the port number is not valid, then an Error is returned (not thrown). (If the input is missing or has the wrong type, an Error object is thrown, since this is a programmer error.)
Parameters
options -- Object, with keys:
input -- String, either an IP address or DNS name, with optional port
suffixresolverConfig -- Object, a set of additional properties to pass to
the resolver constructor.The input string has the form HOSTNAME[:PORT], where the [:PORT] suffix is
optional, and HOSTNAME may be either an IP address or DNS name.
Example: create a resolver that will emit one backend for an instance at IP 127.0.0.1 port 2020:
var resolver = mod_cueball.resolverForIpOrDomain({
'input': '127.0.0.1:2020',
'resolverConfig': {
'recovery': {
'default': {
'retries': 1,
'timeout': 1000,
'delay': 1000,
'maxDelay': 1000
}
}
}
})
/* check whether resolver is an Error */
Example: create a resolver that will track instances associated with DNS
name mydomain.example.com:
var resolver = mod_cueball.resolverForIpOrDomain({
'input': 'mydomain.example.com',
'resolverConfig': {
'recovery': {
'default': {
'retries': 1,
'timeout': 1000,
'delay': 1000,
'maxDelay': 1000
}
}
}
});
/* check whether resolver is an Error */
In these examples, the input string is assumed to come from a user
cueball does the expected thing when given an IP address or DNS name.
Objects returned by a constructor function (such as supplied to the
ConnectionPool constructor) must obey a subset of the node.js socket
interface. In particular they must support the following events and methods:
constructor(backend)Parameters:
backend -- an Object, with properties:
key -- a String, the backend key as supplied via the Resolver interface.
Can be used to uniquely identify the backend.address -- a String, address of the backend (IPv4 or IPv6)port -- a Number, TCP or UDP port numberReturns an object obeying the Connection interface.
connect (required)At construction, the connection object must immediately attempt to make a
connection to the backend specified by the first argument to the constructor.
When the connection succeeds, it must emit the event connect. No arguments are
required.
errorConnection objects may emit error at any time in response to a fatal error.
The connection will be immediately terminated (by calling .destroy()) upon the
emission of any error event.
The error event should be emitted with an Object as the first parameter. This
is expected to have Error on its prototype chain (obj instanceof Error
should be true).
May also be emitted as connectError only in the state before connect has
been emitted.
close (required)Connection objects must emit close as the final event they emit after the
connection has ended. No events may be emitted after close.
#ref() (required)Marks the connection as "referenced", meaning that it should keep the Node process running even if no event handlers are registered on it.
It is generally acceptable for long-lived server processes (which never intend
to exit in normal operation) to provide a Connection that implements ref() and
unref() as no-ops.
#unref() (required)Marks the connection as "unreferenced", allowing the Node process to exit if it is the only remaining source of events.
#destroy() (required)Immediately disconnects the connection and proceeds to emit close.
timeoutOptional. Equivalent to emitting error with a ConnectionTimeoutError as an
argument.
May also be emitted as connectTimeout only in the state before connect has
been emitted.
ClaimTimeoutErrorPassed as first argument to ConnectionPool#claim()'s callback when the given
timeout in options has been exceeded.
Properties
pool -- ConnectionPoolNoBackendsErrorPassed as first argument to ConnectionPool#claim()'s callback when there are
no known backends for the pool and the errorOnEmpty flag is set.
Properties
pool -- ConnectionPoolmod_cueball.poolMonitor.toKangOptions()Returns an options object that can be passed to mod_kang.knStartServer. The
kang options set up snapshots containing a list of all Pool objects in the
system and their associated backends and state.
The returned object is missing the port property, which should be added
before using.
To specify the retry and timeout behaviour of Cueball DNS and pooled connections, the "recovery spec object" is a required argument to most constructors in the API.
A recovery spec object should always have at least one key, named "default",
which gives the default settings for any operation.
More specific per-operation settings can also be given as additional keys.
For example:
{
default: {
timeout: 2000,
retries: 3,
delay: 100
},
dns: {
timeout: 5000,
retries: 3,
delay: 200
}
}
This specifies that DNS-related operations should have a timeout of 5 seconds,
3 retries, and initial delay of 200ms, while all other operations (e.g.
connect() while connecting to a new backend) should have a timeout of 2
seconds, 3 retries and initial delay of 100ms.
The delay field indicates a time to wait between retry attempts. After each
failure, it will be doubled until it exceeds the value of maxDelay.
The possible fields in one operation are:
retries finite Number >= 0, number of retry attemptstimeout finite Number > 0, milliseconds to wait before declaring an
attempt a failuremaxTimeout Number > timeout (can be Infinity), maximum value of
timeout to be reached with exponential timeout increasedelay finite Number >= 0, milliseconds to delay between retry attemptsmaxDelay Number > delay (can be Infinity), maximum value of delay
to be reached with exponential delay increaseAnd the available operations:
dns (all DNS-related operations, lookups etc)dns_srv (specifically lookups on SRV records, this is separate in case you
need to deal with certain old buggy DNS servers that have trouble with SRV)connect (connections to backends in a ConnectionPool)initial (the very first attempt to connect to a new backend, will fall
back to connect if not given)If a given operation has no specification given, it will use default instead.
Resolver instances can operate in a so-called "Dynamic Resolver" mode, where
as well as tracking their particular target service in DNS, they also track the
correct nameservers to ask about it.
This is useful in systems where the nameservers are listed in DNS as a service
just like your ordinary target service (e.g. HTTP). An example is the Joyent
SDC binder. binder acts as a DNS server, listing addresses of all SDC
service instances. This includes listing its own address, and if multiple
binders are deployed, all other binders in the DC.
We can look up the list of currently available binder instances in DNS, and
use this to perform our name resolution. We can also then use the binders to
update our original list of binder instances.
This mode requires a "bootstrap" to begin with, however -- we cannot resolve
the name that the binder instances are listed under until we already know the
address of one of the binders. In Dynamic Resolver mode, cueball will
bootstrap using the system resolvers from /etc/resolv.conf.
const mod_cueball = require('cueball');
const mod_restify = require('restify-clients');
var client = mod_restify.createJsonClient({
url: 'http://napi.coal.joyent.us',
agent: new mod_cueball.HttpAgent({
resolvers: ['binder.coal.joyent.us'],
spares: 4, maximum: 8
})
});
client.get('/networks/' + uuid, function (err, req, res, data) {
...
});
This example code will start by using the system resolvers to resolve
binder.coal.joyent.us. Then, the records found via this lookup will be used
as nameservers to look up napi.coal.joyent.us.
When the TTL expires on the records for binder.coal.joyent.us, we will use
the records from the previous lookup as the list of nameservers to query in
order to find out what the new records should be. Then, we will use any new
nameservers we find for the next napi.coal.joyent.us lookup as well.
Cueball also includes an alternative to the ConnectionPool, named ConnectionSet. This is a more low-level API which is useful for implementing clients for protocols that are not as strictly connection-oriented.
Key differences to ConnectionPool:
ConnectionSets have an identical state graph to ConnectionPools.
new mod_cueball.ConnectionSet(options)Parameters
options -- Object, with keys:
resolver -- Object, an instance of the Resolver interfaceconstructor -- Function, same as in ConnectionPoolrecovery -- Object, a recovery spec (see below)log -- optional Object, a bunyan-style logger to usetarget -- optional Number, target number of connections to be made
available in the entire setmaximum -- optional Number, maximum number of sockets opened by the set.
Note that this number may temporarily be exceeded by 1 socket
to allow the set to re-balance.'added'Emitted when a new connection becomes available in the set. This event must have a handler on it at all times.
Parameters
key -- String, a unique key to identify this connectionconnection -- Object, the connection as returned by the constructorremovedEmitted when an existing connection should be removed from the pool. This event
must have a handler on it at all times. The handler is obligated to take all
necessary actions to drain the connection of outstanding requests and then close
it. The emission of this event must cause the connection object to emit
'close' as soon as possible.
Parameters
key -- String, a unique key to identify the connectionConnectionSet#stop()Stops the ConnectionSet, disconnecting all available connections (by first
emitting 'removed' for them.)
ConnectionSet#setTarget(target)Sets the target number of connections in the ConnectionSet. Will trigger an async operation to add or remove connections in order to meet the new target.
Parameters:
target -- NumberConnectionSet#getConnections()Returns all the currently open connections in the Set, as an Array.
The cbresolve tool is provided to show how cueball would resolve a given
configuration. The output format is not committed. It may change in the
future.
usage: cbresolve HOSTNAME[:PORT] # for DNS-based lookup
cbresolve -S | --static IP[:PORT]... # for static IPs
Locate services in DNS using Cueball resolver.
The following options are available for DNS-based lookups:
-f, --follow periodically re-resolve and report changes
-p, --port PORT default backend port
-r, --resolvers IP[,IP...] list of DNS resolvers
-s, --service SERVICE "service" name (for SRV)
-t, --timeout TIMEOUT timeout for lookups
Example: resolve DNS name "1.moray.us-east.joyent.us":
$ cbresolve 1.moray.emy-10.joyent.us
domain: 1.moray.emy-10.joyent.us
timeout: 5000 milliseconds
172.27.10.218 80 lLbminikNKjfy+iwDobYBuod7Hs=
172.27.10.219 80 iJMaVRehJ2zKfiS55H/lUUFPb9o=
Example: resolve IP/port "127.0.0.1:2020". This is only useful for seeing how cueball would parse your input:
$ cbresolve --static 127.0.0.1:2020
using static IP resolver
127.0.0.1 2020 xBut/f1D52k1TpDN/miW82qXw6k=
**Example: resolve DNS name "1.moray.us-east.joyent.us" and watch for changes:
$ cbresolve --follow 1.moray.emy-10.joyent.us
domain: 1.moray.emy-10.joyent.us
timeout: 5000 milliseconds
2016-06-23T00:45:00.312Z added 172.27.10.218:80 (lLbminikNKjfy+iwDobYBuod7Hs=)
2016-06-23T00:45:00.314Z added 172.27.10.219:80 (iJMaVRehJ2zKfiS55H/lUUFPb9o=)
2016-06-23T00:49:00.478Z removed 172.27.10.218:80 (lLbminikNKjfy+iwDobYBuod7Hs=)
In this example, one of the DNS entries was removed a few minutes after the program was started.
FAQs
manage a pool of connections to a multi-node service where nodes are listed in DNS
The npm package cueball receives a total of 6 weekly downloads. As such, cueball popularity was classified as not popular.
We found that cueball demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 11 open source maintainers collaborating on the project.
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