includes/config/EtcdConfig.php

   1 <?php
   2 /**
   3  * Copyright 2017
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @author Aaron Schulz
  22  */
  23
  24 use Psr\Log\LoggerAwareInterface;
  25 use Psr\Log\LoggerInterface;
  26 use Wikimedia\WaitConditionLoop;
  27
  28 /**
  29  * Interface for configuration instances
  30  *
  31  * @since 1.29
  32  */
  33 class EtcdConfig implements Config, LoggerAwareInterface {
  34         /** @var MultiHttpClient */
  35         private $http;
  36         /** @var BagOStuff */
  37         private $srvCache;
  38         /** @var array */
  39         private $procCache;
  40         /** @var LoggerInterface */
  41         private $logger;
  42
  43         /** @var string */
  44         private $host;
  45         /** @var string */
  46         private $protocol;
  47         /** @var string */
  48         private $directory;
  49         /** @var string */
  50         private $encoding;
  51         /** @var integer */
  52         private $baseCacheTTL;
  53         /** @var integer */
  54         private $skewCacheTTL;
  55         /** @var integer */
  56         private $timeout;
  57         /** @var string */
  58         private $directoryHash;
  59
  60         /**
  61          * @param array $params Parameter map:
  62          *   - host: the host address and port
  63          *   - protocol: either http or https
  64          *   - directory: the etc "directory" were MediaWiki specific variables are located
  65          *   - encoding: one of ("JSON", "YAML"). Defaults to JSON. [optional]
  66          *   - cache: BagOStuff instance or ObjectFactory spec thereof for a server cache.
  67          *            The cache will also be used as a fallback if etcd is down. [optional]
  68          *   - cacheTTL: logical cache TTL in seconds [optional]
  69          *   - skewTTL: maximum seconds to randomly lower the assigned TTL on cache save [optional]
  70          *   - timeout: seconds to wait for etcd before throwing an error [optional]
  71          */
  72         public function __construct( array $params ) {
  73                 $params += [
  74                         'protocol' => 'http',
  75                         'encoding' => 'JSON',
  76                         'cacheTTL' => 10,
  77                         'skewTTL' => 1,
  78                         'timeout' => 10
  79                 ];
  80
  81                 $this->host = $params['host'];
  82                 $this->protocol = $params['protocol'];
  83                 $this->directory = trim( $params['directory'], '/' );
  84                 $this->directoryHash = sha1( $this->directory );
  85                 $this->encoding = $params['encoding'];
  86                 $this->skewCacheTTL = $params['skewTTL'];
  87                 $this->baseCacheTTL = max( $params['cacheTTL'] - $this->skewCacheTTL, 0 );
  88                 $this->timeout = $params['timeout'];
  89
  90                 if ( !isset( $params['cache'] ) ) {
  91                         $this->srvCache = new HashBagOStuff();
  92                 } elseif ( $params['cache'] instanceof BagOStuff ) {
  93                         $this->srvCache = $params['cache'];
  94                 } else {
  95                         $this->srvCache = ObjectFactory::getObjectFromSpec( $params['cache'] );
  96                 }
  97
  98                 $this->logger = new Psr\Log\NullLogger();
  99                 $this->http = new MultiHttpClient( [
 100                         'connTimeout' => $this->timeout,
 101                         'reqTimeout' => $this->timeout
 102                 ] );
 103         }
 104
 105         public function setLogger( LoggerInterface $logger ) {
 106                 $this->logger = $logger;
 107         }
 108
 109         public function has( $name ) {
 110                 $this->load();
 111
 112                 return array_key_exists( $name, $this->procCache['config'] );
 113         }
 114
 115         public function get( $name ) {
 116                 $this->load();
 117
 118                 if ( !array_key_exists( $name, $this->procCache['config'] ) ) {
 119                         throw new ConfigException( "No entry found for '$name'." );
 120                 }
 121
 122                 return $this->procCache['config'][$name];
 123         }
 124
 125         /**
 126          * @throws ConfigException
 127          */
 128         private function load() {
 129                 if ( $this->procCache !== null ) {
 130                         return; // already loaded
 131                 }
 132
 133                 $now = microtime( true );
 134                 $key = $this->srvCache->makeKey( 'variable', $this->directoryHash );
 135
 136                 // Get the cached value or block until it is regenerated (by this or another thread)...
 137                 $data = null; // latest config info
 138                 $error = null; // last error message
 139                 $loop = new WaitConditionLoop(
 140                         function () use ( $key, $now, &$data, &$error ) {
 141                                 // Check if the values are in cache yet...
 142                                 $data = $this->srvCache->get( $key );
 143                                 if ( is_array( $data ) && $data['expires'] > $now ) {
 144                                         $this->logger->debug( "Found up-to-date etcd configuration cache." );
 145
 146                                         return WaitConditionLoop::CONDITION_REACHED;
 147                                 }
 148
 149                                 // Cache is either empty or stale;
 150                                 // refresh the cache from etcd, using a mutex to reduce stampedes...
 151                                 if ( $this->srvCache->lock( $key, 0, $this->baseCacheTTL ) ) {
 152                                         try {
 153                                                 list( $config, $error, $retry ) = $this->fetchAllFromEtcd();
 154                                                 if ( is_array( $config ) ) {
 155                                                         // Avoid having all servers expire cache keys at the same time
 156                                                         $expiry = microtime( true ) + $this->baseCacheTTL;
 157                                                         $expiry += mt_rand( 0, 1e6 ) / 1e6 * $this->skewCacheTTL;
 158
 159                                                         $data = [ 'config' => $config, 'expires' => $expiry ];
 160                                                         $this->srvCache->set( $key, $data, BagOStuff::TTL_INDEFINITE );
 161
 162                                                         $this->logger->info( "Refreshed stale etcd configuration cache." );
 163
 164                                                         return WaitConditionLoop::CONDITION_REACHED;
 165                                                 } else {
 166                                                         $this->logger->error( "Failed to fetch configuration: $error" );
 167                                                         if ( !$retry ) {
 168                                                                 // Fail fast since the error is likely to keep happening
 169                                                                 return WaitConditionLoop::CONDITION_FAILED;
 170                                                         }
 171                                                 }
 172                                         } finally {
 173                                                 $this->srvCache->unlock( $key ); // release mutex
 174                                         }
 175                                 }
 176
 177                                 if ( is_array( $data ) ) {
 178                                         $this->logger->info( "Using stale etcd configuration cache." );
 179
 180                                         return WaitConditionLoop::CONDITION_REACHED;
 181                                 }
 182
 183                                 return WaitConditionLoop::CONDITION_CONTINUE;
 184                         },
 185                         $this->timeout
 186                 );
 187
 188                 if ( $loop->invoke() !== WaitConditionLoop::CONDITION_REACHED ) {
 189                         // No cached value exists and etcd query failed; throw an error
 190                         throw new ConfigException( "Failed to load configuration from etcd: $error" );
 191                 }
 192
 193                 $this->procCache = $data;
 194         }
 195
 196         /**
 197          * @return array (config array or null, error string, allow retries)
 198          */
 199         public function fetchAllFromEtcd() {
 200                 $dsd = new DnsSrvDiscoverer( $this->host );
 201                 $servers = $dsd->getServers();
 202                 if ( !$servers ) {
 203                         return $this->fetchAllFromEtcdServer( $this->host );
 204                 }
 205
 206                 do {
 207                         // Pick a random etcd server from dns
 208                         $server = $dsd->pickServer( $servers );
 209                         $host = IP::combineHostAndPort( $server['target'], $server['port'] );
 210                         // Try to load the config from this particular server
 211                         list( $config, $error, $retry ) = $this->fetchAllFromEtcdServer( $host );
 212                         if ( is_array( $config ) || !$retry ) {
 213                                 break;
 214                         }
 215
 216                         // Avoid the server next time if that failed
 217                         $dsd->removeServer( $server, $servers );
 218                 } while ( $servers );
 219
 220                 return [ $config, $error, $retry ];
 221         }
 222
 223         /**
 224          * @param string $address Host and port
 225          * @return array (config array or null, error string, whether to allow retries)
 226          */
 227         protected function fetchAllFromEtcdServer( $address ) {
 228                 // Retrieve all the values under the MediaWiki config directory
 229                 list( $rcode, $rdesc, /* $rhdrs */, $rbody, $rerr ) = $this->http->run( [
 230                         'method' => 'GET',
 231                         'url' => "{$this->protocol}://{$address}/v2/keys/{$this->directory}/",
 232                         'headers' => [ 'content-type' => 'application/json' ]
 233                 ] );
 234
 235                 static $terminalCodes = [ 404 => true ];
 236                 if ( $rcode < 200 || $rcode > 399 ) {
 237                         return [
 238                                 null,
 239                                 strlen( $rerr ) ? $rerr : "HTTP $rcode ($rdesc)",
 240                                 empty( $terminalCodes[$rcode] )
 241                         ];
 242                 }
 243
 244                 $info = json_decode( $rbody, true );
 245                 if ( $info === null || !isset( $info['node']['nodes'] ) ) {
 246                         return [ null, $rcode, "Unexpected JSON response; missing 'nodes' list.", false ];
 247                 }
 248
 249                 $config = [];
 250                 foreach ( $info['node']['nodes'] as $node ) {
 251                         if ( !empty( $node['dir'] ) ) {
 252                                 continue; // skip directories
 253                         }
 254
 255                         $name = basename( $node['key'] );
 256                         $value = $this->unserialize( $node['value'] );
 257                         if ( !is_array( $value ) || !array_key_exists( 'val', $value ) ) {
 258                                 return [ null, "Failed to parse value for '$name'.", false ];
 259                         }
 260
 261                         $config[$name] = $value['val'];
 262                 }
 263
 264                 return [ $config, null, false ];
 265         }
 266
 267         /**
 268          * @param string $string
 269          * @return mixed
 270          */
 271         private function unserialize( $string ) {
 272                 if ( $this->encoding === 'YAML' ) {
 273                         return yaml_parse( $string );
 274                 } else { // JSON
 275                         return json_decode( $string, true );
 276                 }
 277         }
 278 }