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
  58         /**
  59          * @param array $params Parameter map:
  60          *   - host: the host address and port
  61          *   - protocol: either http or https
  62          *   - directory: the etc "directory" were MediaWiki specific variables are located
  63          *   - encoding: one of ("JSON", "YAML"). Defaults to JSON. [optional]
  64          *   - cache: BagOStuff instance or ObjectFactory spec thereof for a server cache.
  65          *            The cache will also be used as a fallback if etcd is down. [optional]
  66          *   - cacheTTL: logical cache TTL in seconds [optional]
  67          *   - skewTTL: maximum seconds to randomly lower the assigned TTL on cache save [optional]
  68          *   - timeout: seconds to wait for etcd before throwing an error [optional]
  69          */
  70         public function __construct( array $params ) {
  71                 $params += [
  72                         'protocol' => 'http',
  73                         'encoding' => 'JSON',
  74                         'cacheTTL' => 10,
  75                         'skewTTL' => 1,
  76                         'timeout' => 10
  77                 ];
  78
  79                 $this->host = $params['host'];
  80                 $this->protocol = $params['protocol'];
  81                 $this->directory = trim( $params['directory'], '/' );
  82                 $this->encoding = $params['encoding'];
  83                 $this->skewCacheTTL = $params['skewTTL'];
  84                 $this->baseCacheTTL = max( $params['cacheTTL'] - $this->skewCacheTTL, 0 );
  85                 $this->timeout = $params['timeout'];
  86
  87                 if ( !isset( $params['cache'] ) ) {
  88                         $this->srvCache = new HashBagOStuff();
  89                 } elseif ( $params['cache'] instanceof BagOStuff ) {
  90                         $this->srvCache = $params['cache'];
  91                 } else {
  92                         $this->srvCache = ObjectFactory::getObjectFromSpec( $params['cache'] );
  93                 }
  94
  95                 $this->logger = new Psr\Log\NullLogger();
  96                 $this->http = new MultiHttpClient( [
  97                         'connTimeout' => $this->timeout,
  98                         'reqTimeout' => $this->timeout
  99                 ] );
 100         }
 101
 102         public function setLogger( LoggerInterface $logger ) {
 103                 $this->logger = $logger;
 104         }
 105
 106         public function has( $name ) {
 107                 $this->load();
 108
 109                 return array_key_exists( $name, $this->procCache['config'] );
 110         }
 111
 112         public function get( $name ) {
 113                 $this->load();
 114
 115                 if ( !array_key_exists( $name, $this->procCache['config'] ) ) {
 116                         throw new ConfigException( "No entry found for '$name'." );
 117                 }
 118
 119                 return $this->procCache['config'][$name];
 120         }
 121
 122         /**
 123          * @throws ConfigException
 124          */
 125         private function load() {
 126                 if ( $this->procCache !== null ) {
 127                         return; // already loaded
 128                 }
 129
 130                 $now = microtime( true );
 131                 $key = $this->srvCache->makeGlobalKey(
 132                         __CLASS__,
 133                         $this->host,
 134                         $this->directory
 135                 );
 136
 137                 // Get the cached value or block until it is regenerated (by this or another thread)...
 138                 $data = null; // latest config info
 139                 $error = null; // last error message
 140                 $loop = new WaitConditionLoop(
 141                         function () use ( $key, $now, &$data, &$error ) {
 142                                 // Check if the values are in cache yet...
 143                                 $data = $this->srvCache->get( $key );
 144                                 if ( is_array( $data ) && $data['expires'] > $now ) {
 145                                         $this->logger->debug( "Found up-to-date etcd configuration cache." );
 146
 147                                         return WaitConditionLoop::CONDITION_REACHED;
 148                                 }
 149
 150                                 // Cache is either empty or stale;
 151                                 // refresh the cache from etcd, using a mutex to reduce stampedes...
 152                                 if ( $this->srvCache->lock( $key, 0, $this->baseCacheTTL ) ) {
 153                                         try {
 154                                                 list( $config, $error, $retry ) = $this->fetchAllFromEtcd();
 155                                                 if ( is_array( $config ) ) {
 156                                                         // Avoid having all servers expire cache keys at the same time
 157                                                         $expiry = microtime( true ) + $this->baseCacheTTL;
 158                                                         $expiry += mt_rand( 0, 1e6 ) / 1e6 * $this->skewCacheTTL;
 159
 160                                                         $data = [ 'config' => $config, 'expires' => $expiry ];
 161                                                         $this->srvCache->set( $key, $data, BagOStuff::TTL_INDEFINITE );
 162
 163                                                         $this->logger->info( "Refreshed stale etcd configuration cache." );
 164
 165                                                         return WaitConditionLoop::CONDITION_REACHED;
 166                                                 } else {
 167                                                         $this->logger->error( "Failed to fetch configuration: $error" );
 168                                                         if ( !$retry ) {
 169                                                                 // Fail fast since the error is likely to keep happening
 170                                                                 return WaitConditionLoop::CONDITION_FAILED;
 171                                                         }
 172                                                 }
 173                                         } finally {
 174                                                 $this->srvCache->unlock( $key ); // release mutex
 175                                         }
 176                                 }
 177
 178                                 if ( is_array( $data ) ) {
 179                                         $this->logger->info( "Using stale etcd configuration cache." );
 180
 181                                         return WaitConditionLoop::CONDITION_REACHED;
 182                                 }
 183
 184                                 return WaitConditionLoop::CONDITION_CONTINUE;
 185                         },
 186                         $this->timeout
 187                 );
 188
 189                 if ( $loop->invoke() !== WaitConditionLoop::CONDITION_REACHED ) {
 190                         // No cached value exists and etcd query failed; throw an error
 191                         throw new ConfigException( "Failed to load configuration from etcd: $error" );
 192                 }
 193
 194                 $this->procCache = $data;
 195         }
 196
 197         /**
 198          * @return array (config array or null, error string, allow retries)
 199          */
 200         public function fetchAllFromEtcd() {
 201                 $dsd = new DnsSrvDiscoverer( $this->host );
 202                 $servers = $dsd->getServers();
 203                 if ( !$servers ) {
 204                         return $this->fetchAllFromEtcdServer( $this->host );
 205                 }
 206
 207                 do {
 208                         // Pick a random etcd server from dns
 209                         $server = $dsd->pickServer( $servers );
 210                         $host = IP::combineHostAndPort( $server['target'], $server['port'] );
 211                         // Try to load the config from this particular server
 212                         list( $config, $error, $retry ) = $this->fetchAllFromEtcdServer( $host );
 213                         if ( is_array( $config ) || !$retry ) {
 214                                 break;
 215                         }
 216
 217                         // Avoid the server next time if that failed
 218                         $dsd->removeServer( $server, $servers );
 219                 } while ( $servers );
 220
 221                 return [ $config, $error, $retry ];
 222         }
 223
 224         /**
 225          * @param string $address Host and port
 226          * @return array (config array or null, error string, whether to allow retries)
 227          */
 228         protected function fetchAllFromEtcdServer( $address ) {
 229                 // Retrieve all the values under the MediaWiki config directory
 230                 list( $rcode, $rdesc, /* $rhdrs */, $rbody, $rerr ) = $this->http->run( [
 231                         'method' => 'GET',
 232                         'url' => "{$this->protocol}://{$address}/v2/keys/{$this->directory}/",
 233                         'headers' => [ 'content-type' => 'application/json' ]
 234                 ] );
 235
 236                 static $terminalCodes = [ 404 => true ];
 237                 if ( $rcode < 200 || $rcode > 399 ) {
 238                         return [
 239                                 null,
 240                                 strlen( $rerr ) ? $rerr : "HTTP $rcode ($rdesc)",
 241                                 empty( $terminalCodes[$rcode] )
 242                         ];
 243                 }
 244
 245                 $info = json_decode( $rbody, true );
 246                 if ( $info === null || !isset( $info['node']['nodes'] ) ) {
 247                         return [ null, $rcode, "Unexpected JSON response; missing 'nodes' list.", false ];
 248                 }
 249
 250                 $config = [];
 251                 foreach ( $info['node']['nodes'] as $node ) {
 252                         if ( !empty( $node['dir'] ) ) {
 253                                 continue; // skip directories
 254                         }
 255
 256                         $name = basename( $node['key'] );
 257                         $value = $this->unserialize( $node['value'] );
 258                         if ( !is_array( $value ) || !array_key_exists( 'val', $value ) ) {
 259                                 return [ null, "Failed to parse value for '$name'.", false ];
 260                         }
 261
 262                         $config[$name] = $value['val'];
 263                 }
 264
 265                 return [ $config, null, false ];
 266         }
 267
 268         /**
 269          * @param string $string
 270          * @return mixed
 271          */
 272         private function unserialize( $string ) {
 273                 if ( $this->encoding === 'YAML' ) {
 274                         return yaml_parse( $string );
 275                 } else { // JSON
 276                         return json_decode( $string, true );
 277                 }
 278         }
 279 }