Pierre H edited this page Jul 10, 2018 · 15 revisions

This document describes all configuration parameters that determine the behaviour of the crawler and all its components.

Default configuration

The file crawler-default.yaml lists the configuration elements presented below and provides a default value for them. This file is loaded automatically by the sub-classes of ConfigurableTopology and should not be modified. Instead we recommend that you provide a custom configuration file when launching a topology (see below).

Custom configuration

The custom configuration file is expected to be in YAML format and can be passed as a command-line argument as -conf <path_to_config_file> to the Java call of your Main class (which normally would be a sub-class of ConfigurableTopology).

The values in the custom configuration file will override the ones provided in crawler-default.yaml and it does not need to contain all the values.

You can use -conf <path_to_config_file> more than once on the command line, which allows to separate the configuration files for instance between the generic configuration and the configuration of a specific resources.

With Maven installed, you must first generate an uberjar:

mvn clean package

before submitting the topology using the storm command:

storm jar path/to/allmycode.jar -conf my-crawler-conf.yaml -local"

While deploying on a production Storm cluster, simply remove the local parameter.

Passing a configuration file is mandatory. A sample configuration file can be found here.

Configuration options

The following tables describe all available configuration options and their default values. If one of the keys is not present in your YAML file, the default value will be taken.

General options

key default value description
urlfilters.config.file urlfilters.json A JSON configuration file that defines URL filtering strategy. Here is the default implementation. Please also refer to URLFilters. Note: if you want to specify your own file you should give it a different name than urlfilters.json. For more information see here
parsefilters.config.file parsefilters.json The JSON configuration file that defines your ParseFilters. Here is the default one. This influences the behavior of JSoupParserBolt and SiteMapParserBolt. Note: if you want to specify your own file you should give it a different name than parsefilters.json. For more information see here

Fetching and partitioning

key default value description - A name to be part of the User-Agent request header for requests issued by the crawler
http.agent.version - A version to be part of the User-Agent request header for requests issued by the crawler
http.agent.description - A description to be part of the User-Agent request header for requests issued by the crawler
http.agent.url - A URL to be part of the User-Agent request header for requests issued by the crawler (e.g. your Companies Homepage) - An Email address to be part of the User-Agent request header for requests issued by the crawler
http.basicauth.user - A user used for the Basic Authentication implemented in HTTPClient protocole
http.basicauth.password - Password associated with the property http.basicauth.user for the Basic Authentication true not yet implemented - whether or not to store the response time time in the Metadata
http.skip.robots false Generally ignore all robots.txt rules (not recommended) - A SOCKS HTTP proxy server to be used for all requests made by the crawler
http.proxy.port - The port of your SOCKS proxy server
http.timeout 10000 A connection timeout specified in milliseconds. Tuples that run into this timeout will be emitted with the status ERROR in the StatusStream
http.robots.agents '' Comma separated additional user-agent strings to be used for the interpretation of the robots.txt. If left empty (default) than the robots.txt is interpreted with the value of
http.use.cookies false Use cookies from the repsonse in requests sent to direct child links.
http.content.limit -1 The maximum number of bytes for returned HTTP response bodies. By default no limit is applied. In the generated archetype a limit of 65536 is present.
partition.url.mode byHost Possible values are: byHost, byDomain, byIP. Defines how URLs are partitioned and by that routed to the FetcherBolt. For example byIP would lead to all tuples with a URL that is served by the same IP address to be always (for the lifetime of your topology) fetched by the same Storm task. This partitioning is important because it makes things like e.g. caching a robots.txt file for a specific domain very efficient. The value you specify here is being used to make use of Storms Field Grouping.
fetcher.queue.mode byHost ??? Possible values are: byHost, byDomain, byIP. This parameter influences how FetchQueues are grouped inside the FetcherBolt. This influences the overall thread count and things like crawl delays (see below)
fetcher.max.crawl.delay 30 The maximum number in seconds that will be accepted by Crawl-delay directives in robots.txt files. If the crawl-delay exceeds this value the behavior depends on the value of fetcher.max.crawl.delay.force.
fetcher.max.crawl.delay.force false Configures the behavior of fetcher if the robots.txt crawl-delay exceeds fetcher.max.crawl.delay. If false: the tuple is emitted to the StatusStream as an ERROR. If true: the queue delay is set to fetcher.max.crawl.delay.
fetcher.threads.per.queue 1 The default number of threads per queue. This can be overwritten for specific hosts/domains/IPs. See below fetcher.threads. per.queue Overwrites the default value of fetcher.threads.per.queue. This is very useful if you have domains/hosts/IPs that you want to crawl more intensively (e.g. because they a lot of URLs emitted by your Spout
fetcher.server.delay 1 Defines delay between crawls in the same queue if no Craw-delay is defines for this URL in the pages robots.txt. Note: For multi-threaded queues neither this value nor the one from the robots.txt will be honored. See fetcher.server.min.delay.
fetcher.server.min.delay 0 ??? Defines the delay between crawls in the same queue if a queue has > 1 thread. The Crawl-delay declared in the robots.txt is ignored in this case and this value is taken.
fetcher.server.delay.force false Defines the behavior of fetcher when the crawl-delay in the robots.txt is smaller than the value configured in fetcher.server.delay. If false the shorter crawl-delay from the robots.txt is used. If true the longer configured delay is forced.
fetcher.threads.number 10 The number of threads that fetch pages from all queues concurrently. This threads does the actual work of downloading the page. Increase this to get more throughput at a cost of higher network, CPU and memory utilisation. Tweak this value carefully while looking at your system resources to find a value that works best for your hardware and network infrastructure.
redirections.allowed true If URL redirects are allowed or not. If set to true, the crawler will emit the targeted URL in the StatusStream with the status DISCOVERED
http.robots.403.allow true ??? Defines what happens in the scenario where the request to the robots.txt file is being responded with a HTTP 403 (Forbidden). When set to true this means that the crawler would not be limited at all and freely crawl all pages of the domain. If set to false this means that the crawler would not fetch any of the pages for this domain.
protocols http,https The protocols to support. Each of them has a corresponding <proto>.protocol.implementation directive. Don't touch this unless you are implementing additional protocols to be supported.
http.protocol.implementation com.digitalpebble.stormcrawler.protocol. httpclient.HttpProtocol The Protocol implementation for plain HTTP
https.protocol.implementation com.digitalpebble.stormcrawler.protocol. httpclient.HttpProtocol The Protocol implementation for HTTP over SSL


The values below are used by sub-classes of AbstractIndexerBolt. Examples: StdOut, ElasticSearch. These classes persist the outcome of your crawling process and receive tuples enriched with Metadata (with all information gathered by previous Bolts)

key default value description - A YAML List of key=value strings that let you filter records that should be index based on Metadata of a tuple. If specified, only tuples that match the given filter are being indexed. This is just used by the helper method AbstractIndexerBolt.filterDocument(Metadata). Using this method is on the responsibility of the implementing class. [Here is an example] ( - A YAML List of key=value strings that let you define a mapping of fields that occur in the Metadata of a tuple to field-names for your persistence layer. The AbstractIndexerBolt provides a method names filterMetadata(Metadata) that sub-classes should use inside their execute() method in order to apply this mapping to the Metadata object. Here is an example.
indexer.text.fieldname - The fieldname that should be used to index the content of HTML body. The usage of this is again in the responsibility of the class that extends AbstractIndexerBolt. The value of this can be accessed using the protected method fieldNameForText(). Here is an example.
indexer.url.fieldname - Same as above - indexer.text.fieldname just for the URL Field

Status persistence

This refers to persisting the status of a URL (e.g. ERROR, DISCOVERED etc.) along with a something like a nextFetchDate that is being calculated by a Scheduler

key default value description
status.updater.use.cache true Using this cache helps to prevent persisting the same URLs over and over again. The store() method of your implementation of AbstractStatusUpdaterBolt (example) is only called if a URL does not already exist in the cache. This is a simple but efficient improvement to avoid re-persisting e.g. the same internal links over and over again.
status.updater.cache.spec maximumSize=10000, expireAfterAccess=1h A cache specification string that defines the size and behavior of the above cache.
fetchInterval.default 1440 In minutes - how to schedule re-visits of pages. 1 Day by default. This is used by the DefaultScheduler. If you need customized scheduling logic, just implement your own Scheduler. Note: the Scheduler class is not yet configurable. See or update (this issue)[] if you need this bahvior. Should be quite easy to make the implemetation class configurable.
fetchInterval.fetch.error 120 In minutes - how often to re-visit pages with a fetch error. Every two hours by default. Identified by tuples in the (StatusStream)[] with the state of FETCH_ERROR
fetchInterval.error 44640 In minutes - how often to re-visit pages with an error (HTTP 4XX or 5XX). Every month by default. Identified by tuples in the (StatusStream)[] with the state of ERROR.


key default value description
parser.emitOutlinks true Whether or not to emit outgoing links found in the parsed HTML document to the StatusStrean as DISCOVERED. Your URL Filters are applied to outgoing links before they are emitted. This option being true is crucial if you are building a recursive crawler.
track.anchors true Whether or not to add the anchor text (can be > 1) of (filtered) outgoing links with the key anchors to the Metadata of a tuple.


key default value description
metadata.track.path true Whether or not to track the URL path of outgoing links (all URLs that the crawler crawled to find this link) in the Metadata. The Metadata field name for this is url.path. It's a list of URLs that represent the crawl path (how did the crawler find this page).
metadata.track.depth true Whether or not to track the depth of a crawled URL. This is a simple counter that is being tracked for outgoing links in the Metadata and incremented by 1 for every page that was crawled to find a specific link. This can be useful to let your Spout decide/sort which URLs to emit based on their depth. You could use this to influence the behavior of your recursive crawl (e.g. prefer pages with a low depth count).
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