NAME¶

carbon-c-relay - graphite relay, aggregator and rewriter

SYNOPSIS¶

carbon-c-relay -f config-file [ options ... ]

DESCRIPTION¶

carbon-c-relay accepts, cleanses, matches, rewrites, forwards and aggregates graphite metrics by listening for incoming connections and relaying the messages to other servers defined in its configuration. The core functionality is to route messages via flexible rules to the desired destinations.

carbon-c-relay is a simple program that reads its routing information from a file. The command line arguments allow to set the location for this file, as well as the amount of dispatchers (worker threads) to use for reading the data from incoming connections and passing them onto the right destination(s). The route file supports two main constructs: clusters and matches. The first define groups of hosts data metrics can be sent to, the latter define which metrics should be sent to which cluster. Aggregation rules are seen as matches. Rewrites are actions that directly affect the metric at the point in which they appear in the configuration.

For every metric received by the relay, cleansing is performed. The following changes are performed before any match, aggregate or rewrite rule sees the metric:

• double dot elimination (necessary for correctly functioning consistent hash routing)
• trailing/leading dot elimination
• whitespace normalisation (this mostly affects output of the relay to other targets: metric, value and timestamp will be separated by a single space only, ever)
• irregular char replacement with underscores (_), currently irregular is defined as not being in [0-9a-zA-Z-_:#], but can be overridden on the command line. Note that tags (when present and allowed) are not processed this way.

OPTIONS¶

These options control the behaviour of carbon-c-relay.

• -v: Print version string and exit.
• -d: Enable debug mode, this prints statistics to stdout and prints extra messages about some situations encountered by the relay that normally would be too verbose to be enabled. When combined with -t (test mode) this also prints stub routes and consistent-hash ring contents.
• -s: Enable submission mode. In this mode, internal statistics are not generated. Instead, queue pressure and metrics drops are reported on stdout. This mode is useful when used as submission relay which´ job is just to forward to (a set of) main relays. Statistics about the submission relays in this case are not needed, and could easily cause a non-desired flood of metrics e.g. when used on each and every host locally.
• -t: Test mode. This mode doesn´t do any routing at all, but instead reads input from stdin and prints what actions would be taken given the loaded configuration. This mode is very useful for testing relay routes for regular expression syntax etc. It also allows to give insight on how routing is applied in complex configurations, for it shows rewrites and aggregates taking place as well. When -t is repeated, the relay will only test the configuration for validity and exit immediately afterwards. Any standard output is suppressed in this mode, making it ideal for start-scripts to test a (new) configuration.
• -f config-file: Read configuration from config-file. A configuration consists of clusters and routes. See CONFIGURATION SYNTAX for more information on the options and syntax of this file.
• -l log-file: Use log-file for writing messages. Without this option, the relay writes both to stdout and stderr. When logging to file, all messages are prefixed with MSG when they were sent to stdout, and ERR when they were sent to stderr.
• -p port: Listen for connections on port port. The port number is used for both TCP, UDP and UNIX sockets. In the latter case, the socket file contains the port number. The port defaults to 2003, which is also used by the original carbon-cache.py. Note that this only applies to the defaults, when listen directives are in the config, this setting is ignored.
• -w workers: Use workers number of threads. The default number of workers is equal to the amount of detected CPU cores. It makes sense to reduce this number on many-core machines, or when the traffic is low.
• -b batchsize: Set the amount of metrics that sent to remote servers at once to batchsize. When the relay sends metrics to servers, it will retrieve batchsize metrics from the pending queue of metrics waiting for that server and send those one by one. The size of the batch will have minimal impact on sending performance, but it controls the amount of lock-contention on the queue. The default is 2500.
• -q queuesize: Each server from the configuration where the relay will send metrics to, has a queue associated with it. This queue allows for disruptions and bursts to be handled. The size of this queue will be set to queuesize which allows for that amount of metrics to be stored in the queue before it overflows, and the relay starts dropping metrics. The larger the queue, more metrics can be absorbed, but also more memory will be used by the relay. The default queue size is 25000.
• -L stalls: Sets the max mount of stalls to stalls before the relay starts dropping metrics for a server. When a queue fills up, the relay uses a mechanism called stalling to signal the client (writing to the relay) of this event. In particular when the client sends a large amount of metrics in very short time (burst), stalling can help to avoid dropping metrics, since the client just needs to slow down for a bit, which in many cases is possible (e.g. when catting a file with nc(1)). However, this behaviour can also obstruct, artificially stalling writers which cannot stop that easily. For this the stalls can be set from 0 to 15, where each stall can take around 1 second on the client. The default value is set to 4, which is aimed at the occasional disruption scenario and max effort to not loose metrics with moderate slowing down of clients.
• -C CAcertpath: Read CA certs (for use with TLS/SSL connections) from given path or file. When not given, the default locations are used. Strict verfication of the peer is performed, so when using self-signed certificates, be sure to include the CA cert in the default location, or provide the path to the cert using this option.
• -T timeout: Specifies the IO timeout in milliseconds used for server connections. The default is 600 milliseconds, but may need increasing when WAN links are used for target servers. A relatively low value for connection timeout allows the relay to quickly establish a server is unreachable, and as such failover strategies to kick in before the queue runs high.
• -c chars: Defines the characters that are next to [A-Za-z0-9] allowed in metrics to chars. Any character not in this list, is replaced by the relay with _ (underscore). The default list of allowed characters is -_:#.
• -m length: Limits the metric names to be of at most length bytes long. Any lines containing metric names larger than this will be discarded.
• -M length Limits the input to lines of at most length bytes. Any excess lines will be discarded. Note that -m needs to be smaller than this value.
• -H hostname: Override hostname determined by a call to gethostname(3) with hostname. The hostname is used mainly in the statistics metrics carbon.relays.<hostname>.<...> sent by the relay.
• -B backlog: Sets TCP connection listen backlog to backlog connections. The default value is 32 but on servers which receive many concurrent connections, this setting likely needs to be increased to avoid connection refused errors on the clients.
• -U bufsize: Sets the socket send/receive buffer sizes in bytes, for both TCP and UDP scenarios. When unset, the OS default is used. The maximum is also determined by the OS. The sizes are set using setsockopt with the flags SO_RCVBUF and SO_SNDBUF. Setting this size may be necessary for large volume scenarios, for which also -B might apply. Checking the Recv-Q and the receive errors values from netstat gives a good hint about buffer usage.
• -E: Disable disconnecting idle incoming connections. By default the relay disconnects idle client connections after 10 minutes. It does this to prevent resources clogging up when a faulty or malicious client keeps on opening connections without closing them. It typically prevents running out of file descriptors. For some scenarios, however, it is not desirable for idle connections to be disconnected, hence passing this flag will disable this behaviour.
• -D: Deamonise into the background after startup. This option requires -l and -P flags to be set as well.
• -P pidfile: Write the pid of the relay process to a file called pidfile. This is in particular useful when daemonised in combination with init managers.
• -O threshold: The minimum number of rules to find before trying to optimise the ruleset. The default is 50, to disable the optimiser, use -1, to always run the optimiser use 0. The optimiser tries to group rules to avoid spending excessive time on matching expressions.

CONFIGURATION SYNTAX¶

The config file supports the following syntax, where comments start with a # character and can appear at any position on a line and suppress input until the end of that line:

cluster <name>


    < <forward | any_of | failover> [useall] |


      <carbon_ch | fnv1a_ch | jump_fnv1a_ch> [replication <count>] [dynamic] >


        <host[:port][=instance] [proto <udp | tcp>]


                                [type linemode]


                                [transport <plain | gzip | lz4 | snappy>


                                           [ssl]]> ...


    ;
cluster <name>


    file [ip]


        </path/to/file> ...


    ;
match


        <* | expression ...>


    [validate <expression> else <log | drop>]


    send to <cluster ... | blackhole>


    [stop]


    ;
rewrite <expression>


    into <replacement>


    ;
aggregate


        <expression> ...


    every <interval> seconds


    expire after <expiration> seconds


    [timestamp at <start | middle | end> of bucket]


    compute <sum | count | max | min | average |


             median | percentile<%> | variance | stddev> write to


        <metric>


    [compute ...]


    [send to <cluster ...>]


    [stop]


    ;
send statistics to <cluster ...>


    [stop]


    ;
statistics


    [submit every <interval> seconds]


    [reset counters after interval]


    [prefix with <prefix>]


    [send to <cluster ...>]


    [stop]


    ;
listen


    type linemode [transport <plain | gzip | lz4 | snappy> [ssl <pemcert>]]


        <<interface[:port] | port> proto <udp | tcp>> ...


        </ptah/to/file proto unix> ...


    ;
include </path/to/file/or/glob>


    ;

EXAMPLES¶

carbon-c-relay evolved over time, growing features on demand as the tool proved to be stable and fitting the job well. Below follow some annotated examples of constructs that can be used with the relay.

Clusters can be defined as much as necessary. They receive data from match rules, and their type defines which members of the cluster finally get the metric data. The simplest cluster form is a forward cluster:

cluster send-through


    forward


        10.1.0.1


    ;

Any metric sent to the send-through cluster would simply be forwarded to the server at IPv4 address 10.1.0.1. If we define multiple servers, all of those servers would get the same metric, thus:

cluster send-through


    forward


        10.1.0.1


        10.2.0.1


    ;

The above results in a duplication of metrics send to both machines. This can be useful, but most of the time it is not. The any_of cluster type is like forward, but it sends each incoming metric to any of the members. The same example with such cluster would be:

cluster send-to-any-one


    any_of 10.1.0.1:2010 10.1.0.1:2011;

This would implement a multipath scenario, where two servers are used, the load between them is spread, but should any of them fail, all metrics are sent to the remaining one. This typically works well for upstream relays, or for balancing carbon-cache processes running on the same machine. Should any member become unavailable, for instance due to a rolling restart, the other members receive the traffic. If it is necessary to have true fail-over, where the secondary server is only used if the first is down, the following would implement that:

cluster try-first-then-second


    failover 10.1.0.1:2010 10.1.0.1:2011;

These types are different from the two consistent hash cluster types:

cluster graphite


    carbon_ch


        127.0.0.1:2006=a


        127.0.0.1:2007=b


        127.0.0.1:2008=c


    ;

If a member in this example fails, all metrics that would go to that member are kept in the queue, waiting for the member to return. This is useful for clusters of carbon-cache machines where it is desirable that the same metric ends up on the same server always. The carbon_ch cluster type is compatible with carbon-relay consistent hash, and can be used for existing clusters populated by carbon-relay. For new clusters, however, it is better to use the fnv1a_ch cluster type, for it is faster, and allows to balance over the same address but different ports without an instance number, in constrast to carbon_ch.

Because we can use multiple clusters, we can also replicate without the use of the forward cluster type, in a more intelligent way:

cluster dc-old


    carbon_ch replication 2


        10.1.0.1


        10.1.0.2


        10.1.0.3


    ;
cluster dc-new1


    fnv1a_ch replication 2


        10.2.0.1


        10.2.0.2


        10.2.0.3


    ;
cluster dc-new2


    fnv1a_ch replication 2


        10.3.0.1


        10.3.0.2


        10.3.0.3


    ;
match *


    send to dc-old


    ;
match *


    send to


        dc-new1


        dc-new2


    stop


    ;

In this example all incoming metrics are first sent to dc-old, then dc-new1 and finally to dc-new2. Note that the cluster type of dc-old is different. Each incoming metric will be send to 2 members of all three clusters, thus replicating to in total 6 destinations. For each cluster the destination members are computed independently. Failure of clusters or members does not affect the others, since all have individual queues. The above example could also be written using three match rules for each dc, or one match rule for all three dcs. The difference is mainly in performance, the number of times the incoming metric has to be matched against an expression. The stop rule in dc-new match rule is not strictly necessary in this example, because there are no more following match rules. However, if the match would target a specific subset, e.g. ^sys\., and more clusters would be defined, this could be necessary, as for instance in the following abbreviated example:

cluster dc1-sys ... ;
cluster dc2-sys ... ;
cluster dc1-misc ... ;
cluster dc2-misc ... ;
match ^sys\. send to dc1-sys;
match ^sys\. send to dc2-sys stop;
match * send to dc1-misc;
match * send to dc2-misc stop;

As can be seen, without the stop in dc2-sys´ match rule, all metrics starting with sys. would also be send to dc1-misc and dc2-misc. It can be that this is desired, of course, but in this example there is a dedicated cluster for the sys metrics.

Suppose there would be some unwanted metric that unfortunately is generated, let´s assume some bad/old software. We don´t want to store this metric. The blackhole cluster is suitable for that, when it is harder to actually whitelist all wanted metrics. Consider the following:

match


        some_legacy1$


        some_legacy2$


    send to blackhole


    stop;

This would throw away all metrics that end with some_legacy, that would otherwise be hard to filter out. Since the order matters, it can be used in a construct like this:

cluster old ... ;
cluster new ... ;
match * send to old;
match unwanted send to blackhole stop;
match * send to new;

In this example the old cluster would receive the metric that´s unwanted for the new cluster. So, the order in which the rules occur does matter for the execution.

Validation can be used to ensure the data for metrics is as expected. A global validation for just number (no floating point) values could be:

match *


    validate ^[0-9]+\ [0-9]+$ else drop


    ;

(Note the escape with backslash \ of the space, you might be able to use \s or [:space:] instead, this depends on your configured regex implementation.)

The validation clause can exist on every match rule, so in principle, the following is valid:

match ^foo


    validate ^[0-9]+\ [0-9]+$ else drop


    send to integer-cluster


    ;
match ^foo


    validate ^[0-9.e+-]+\ [0-9.e+-]+$ else drop


    send to float-cluster


    stop;

Note that the behaviour is different in the previous two examples. When no send to clusters are specified, a validation error makes the match behave like the stop keyword is present. Likewise, when validation passes, processing continues with the next rule. When destination clusters are present, the match respects the stop keyword as normal. When specified, processing will always stop when specified so. However, if validation fails, the rule does not send anything to the destination clusters, the metric will be dropped or logged, but never sent.

The relay is capable of rewriting incoming metrics on the fly. This process is done based on regular expressions with capture groups that allow to substitute parts in a replacement string. Rewrite rules allow to cleanup metrics from applications, or provide a migration path. In it´s simplest form a rewrite rule looks like this:

rewrite ^server\.(.+)\.(.+)\.([a-zA-Z]+)([0-9]+)


    into server.\_1.\2.\3.\3\4


    ;

In this example a metric like server.DC.role.name123 would be transformed into server.dc.role.name.name123. For rewrite rules hold the same as for matches, that their order matters. Hence to build on top of the old/new cluster example done earlier, the following would store the original metric name in the old cluster, and the new metric name in the new cluster:

match * send to old;
rewrite ... ;
match * send to new;

Note that after the rewrite, the original metric name is no longer available, as the rewrite happens in-place.

Aggregations are probably the most complex part of carbon-c-relay. Two ways of specifying aggregates are supported by carbon-c-relay. The first, static rules, are handled by an optimiser which tries to fold thousands of rules into groups to make the matching more efficient. The second, dynamic rules, are very powerful compact definitions with possibly thousands of internal instantiations. A typical static aggregation looks like:

aggregate


        ^sys\.dc1\.somehost-[0-9]+\.somecluster\.mysql\.replication_delay


        ^sys\.dc2\.somehost-[0-9]+\.somecluster\.mysql\.replication_delay


    every 10 seconds


    expire after 35 seconds


    timestamp at end of bucket


    compute sum write to


        mysql.somecluster.total_replication_delay


    compute average write to


        mysql.somecluster.average_replication_delay


    compute max write to


        mysql.somecluster.max_replication_delay


    compute count write to


        mysql.somecluster.replication_delay_metric_count


    ;

In this example, four aggregations are produced from the incoming matching metrics. In this example we could have written the two matches as one, but for demonstration purposes we did not. Obviously they can refer to different metrics, if that makes sense. The every 10 seconds clause specifies in what interval the aggregator can expect new metrics to arrive. This interval is used to produce the aggregations, thus each 10 seconds 4 new metrics are generated from the data received sofar. Because data may be in transit for some reason, or generation stalled, the expire after clause specifies how long the data should be kept before considering a data bucket (which is aggregated) to be complete. In the example, 35 was used, which means after 35 seconds the first aggregates are produced. It also means that metrics can arrive 35 seconds late, and still be taken into account. The exact time at which the aggregate metrics are produced is random between 0 and interval (10 in this case) seconds after the expiry time. This is done to prevent thundering herds of metrics for large aggregation sets. The timestamp that is used for the aggregations can be specified to be the start, middle or end of the bucket. Original carbon-aggregator.py uses start, while carbon-c-relay´s default has always been end. The compute clauses demonstrate a single aggregation rule can produce multiple aggregates, as often is the case. Internally, this comes for free, since all possible aggregates are always calculated, whether or not they are used. The produced new metrics are resubmitted to the relay, hence matches defined before in the configuration can match output of the aggregator. It is important to avoid loops, that can be generated this way. In general, splitting aggregations to their own carbon-c-relay instance, such that it is easy to forward the produced metrics to another relay instance is a good practice.

The previous example could also be written as follows to be dynamic:

aggregate


        ^sys\.dc[0-9].(somehost-[0-9]+)\.([^.]+)\.mysql\.replication_delay


    every 10 seconds


    expire after 35 seconds


    compute sum write to


        mysql.host.\1.replication_delay


    compute sum write to


        mysql.host.all.replication_delay


    compute sum write to


        mysql.cluster.\2.replication_delay


    compute sum write to


        mysql.cluster.all.replication_delay


    ;

Here a single match, results in four aggregations, each of a different scope. In this example aggregation based on hostname and cluster are being made, as well as the more general all targets, which in this example have both identical values. Note that with this single aggregation rule, both per-cluster, per-host and total aggregations are produced. Obviously, the input metrics define which hosts and clusters are produced.

With use of the send to clause, aggregations can be made more intuitive and less error-prone. Consider the below example:

cluster graphite fnv1a_ch ip1 ip2 ip3;
aggregate ^sys\.somemetric


    every 60 seconds


    expire after 75 seconds


    compute sum write to


        sys.somemetric


    send to graphite


    stop


    ;
match * send to graphite;

It sends all incoming metrics to the graphite cluster, except the sys.somemetric ones, which it replaces with a sum of all the incoming ones. Without a stop in the aggregate, this causes a loop, and without the send to, the metric name can´t be kept its original name, for the output now directly goes to the cluster.

STATISTICS¶

When carbon-c-relay is run without -d or -s arguments, statistics will be produced. By default they are sent to the relay itself in the form of carbon.relays.<hostname>.*. See the statistics construct to override this prefix, sending interval and values produced. While many metrics have a similar name to what carbon-cache.py would produce, their values are likely different. By default, most values are running counters which only increase over time. The use of the nonNegativeDerivative() function from graphite is useful with these.

The following metrics are produced under the carbon.relays.<hostname> namespace:

•

metricsReceived

The number of metrics that were received by the relay. Received here means that they were seen and processed by any of the dispatchers.

•

metricsSent

The number of metrics that were sent from the relay. This is a total count for all servers combined. When incoming metrics are duplicated by the cluster configuration, this counter will include all those duplications. In other words, the amount of metrics that were successfully sent to other systems. Note that metrics that are processed (received) but still in the sending queue (queued) are not included in this counter.

•

metricsDiscarded

The number of input lines that were not considered to be a valid metric. Such lines can be empty, only containing whitespace, or hitting the limits given for max input length and/or max metric length (see -m and -M options).

•

metricsQueued

The total number of metrics that are currently in the queues for all the server targets. This metric is not cumulative, for it is a sample of the queue size, which can (and should) go up and down. Therefore you should not use the derivative function for this metric.

•

metricsDropped

The total number of metric that had to be dropped due to server queues overflowing. A queue typically overflows when the server it tries to send its metrics to is not reachable, or too slow in ingesting the amount of metrics queued. This can be network or resource related, and also greatly depends on the rate of metrics being sent to the particular server.

•

metricsBlackholed

The number of metrics that did not match any rule, or matched a rule with blackhole as target. Depending on your configuration, a high value might be an indication of a misconfiguration somewhere. These metrics were received by the relay, but never sent anywhere, thus they disappeared.

•

metricStalls

The number of times the relay had to stall a client to indicate that the downstream server cannot handle the stream of metrics. A stall is only performed when the queue is full and the server is actually receptive of metrics, but just too slow at the moment. Stalls typically happen during micro-bursts, where the client typically is unaware that it should stop sending more data, while it is able to.

•

connections

The number of connect requests handled. This is an ever increasing number just counting how many connections were accepted.

•

disconnects

The number of disconnected clients. A disconnect either happens because the client goes away, or due to an idle timeout in the relay. The difference between this metric and connections is the amount of connections actively held by the relay. In normal situations this amount remains within reasonable bounds. Many connections, but few disconnections typically indicate a possible connection leak in the client. The idle connections disconnect in the relay here is to guard against resource drain in such scenarios.

•

dispatch_wallTime_us

The number of microseconds spent by the dispatchers to do their work. In particular on multi-core systems, this value can be confusing, however, it indicates how long the dispatchers were doing work handling clients. It includes everything they do, from reading data from a socket, cleaning up the input metric, to adding the metric to the appropriate queues. The larger the configuration, and more complex in terms of matches, the more time the dispatchers will spend on the cpu. But also time they do /not/ spend on the cpu is included in this number. It is the pure wallclock time the dispatcher was serving a client.

•

dispatch_sleepTime_us

The number of microseconds spent by the dispatchers sleeping waiting for work. When this value gets small (or even zero) the dispatcher has so much work that it doesn´t sleep any more, and likely can´t process the work in a timely fashion any more. This value plus the wallTime from above sort of sums up to the total uptime taken by this dispatcher. Therefore, expressing the wallTime as percentage of this sum gives the busyness percentage draining all the way up to 100% if sleepTime goes to 0.

•

server_wallTime_us

The number of microseconds spent by the servers to send the metrics from their queues. This value includes connection creation, reading from the queue, and sending metrics over the network.

•

dispatcherX

For each indivual dispatcher, the metrics received and blackholed plus the wall clock time. The values are as described above.

•

destinations.X

For all known destinations, the number of dropped, queued and sent metrics plus the wall clock time spent. The values are as described above.

•

aggregators.metricsReceived

The number of metrics that were matched an aggregator rule and were accepted by the aggregator. When a metric matches multiple aggregators, this value will reflect that. A metric is not counted when it is considered syntactically invalid, e.g. no value was found.

•

aggregators.metricsDropped

The number of metrics that were sent to an aggregator, but did not fit timewise. This is either because the metric was too far in the past or future. The expire after clause in aggregate statements controls how long in the past metric values are accepted.

•

aggregators.metricsSent

The number of metrics that were sent from the aggregators. These metrics were produced and are the actual results of aggregations.

BUGS¶

Please report them at: https://github.com/grobian/carbon-c-relay/issues

AUTHOR¶

Fabian Groffen <grobian@gentoo.org>

SEE ALSO¶

All other utilities from the graphite stack.

This project aims to be a fast replacement of the original Carbon relay http://graphite.readthedocs.org/en/1.0/carbon-daemons.html#carbon-relay-py. carbon-c-relay aims to deliver performance and configurability. Carbon is single threaded, and sending metrics to multiple consistent-hash clusters requires chaining of relays. This project provides a multithreaded relay which can address multiple targets and clusters for each and every metric based on pattern matches.

There are a couple more replacement projects out there, which are carbon-relay-ng https://github.com/graphite-ng/carbon-relay-ng and graphite-relay https://github.com/markchadwick/graphite-relay.

Compared to carbon-relay-ng, this project does provide carbon´s consistent-hash routing. graphite-relay, which does this, however doesn´t do metric-based matches to direct the traffic, which this project does as well. To date, carbon-c-relay can do aggregations, failover targets and more.

ACKNOWLEDGEMENTS¶

This program was originally developed for Booking.com, which approved that the code was published and released as Open Source on GitHub, for which the author would like to express his gratitude. Development has continued since with the help of many contributors suggesting features, reporting bugs, adding patches and more to make carbon-c-relay into what it is today.