includes/config/EtcdConfig.php

   1 <?php
   2 /**
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  16  * http://www.gnu.org/copyleft/gpl.html
  17  *
  18  * @file
  19  */
  20
  21 use Psr\Log\LoggerAwareInterface;
  22 use Psr\Log\LoggerInterface;
  23 use Wikimedia\WaitConditionLoop;
  24
  25 /**
  26  * Interface for configuration instances
  27  *
  28  * @since 1.29
  29  */
  30 class EtcdConfig implements Config, LoggerAwareInterface {
  31         /** @var MultiHttpClient */
  32         private $http;
  33         /** @var BagOStuff */
  34         private $srvCache;
  35         /** @var array */
  36         private $procCache;
  37         /** @var LoggerInterface */
  38         private $logger;
  39
  40         /** @var string */
  41         private $host;
  42         /** @var string */
  43         private $protocol;
  44         /** @var string */
  45         private $directory;
  46         /** @var string */
  47         private $encoding;
  48         /** @var int */
  49         private $baseCacheTTL;
  50         /** @var int */
  51         private $skewCacheTTL;
  52         /** @var int */
  53         private $timeout;
  54
  55         /**
  56          * @param array $params Parameter map:
  57          *   - host: the host address and port
  58          *   - protocol: either http or https
  59          *   - directory: the etc "directory" were MediaWiki specific variables are located
  60          *   - encoding: one of ("JSON", "YAML"). Defaults to JSON. [optional]
  61          *   - cache: BagOStuff instance or ObjectFactory spec thereof for a server cache.
  62          *            The cache will also be used as a fallback if etcd is down. [optional]
  63          *   - cacheTTL: logical cache TTL in seconds [optional]
  64          *   - skewTTL: maximum seconds to randomly lower the assigned TTL on cache save [optional]
  65          *   - timeout: seconds to wait for etcd before throwing an error [optional]
  66          */
  67         public function __construct( array $params ) {
  68                 $params += [
  69                         'protocol' => 'http',
  70                         'encoding' => 'JSON',
  71                         'cacheTTL' => 10,
  72                         'skewTTL' => 1,
  73                         'timeout' => 2
  74                 ];
  75
  76                 $this->host = $params['host'];
  77                 $this->protocol = $params['protocol'];
  78                 $this->directory = trim( $params['directory'], '/' );
  79                 $this->encoding = $params['encoding'];
  80                 $this->skewCacheTTL = $params['skewTTL'];
  81                 $this->baseCacheTTL = max( $params['cacheTTL'] - $this->skewCacheTTL, 0 );
  82                 $this->timeout = $params['timeout'];
  83
  84                 if ( !isset( $params['cache'] ) ) {
  85                         $this->srvCache = new HashBagOStuff();
  86                 } elseif ( $params['cache'] instanceof BagOStuff ) {
  87                         $this->srvCache = $params['cache'];
  88                 } else {
  89                         $this->srvCache = ObjectFactory::getObjectFromSpec( $params['cache'] );
  90                 }
  91
  92                 $this->logger = new Psr\Log\NullLogger();
  93                 $this->http = new MultiHttpClient( [
  94                         'connTimeout' => $this->timeout,
  95                         'reqTimeout' => $this->timeout,
  96                         'logger' => $this->logger
  97                 ] );
  98         }
  99
 100         public function setLogger( LoggerInterface $logger ) {
 101                 $this->logger = $logger;
 102                 $this->http->setLogger( $logger );
 103         }
 104
 105         public function has( $name ) {
 106                 $this->load();
 107
 108                 return array_key_exists( $name, $this->procCache['config'] );
 109         }
 110
 111         public function get( $name ) {
 112                 $this->load();
 113
 114                 if ( !array_key_exists( $name, $this->procCache['config'] ) ) {
 115                         throw new ConfigException( "No entry found for '$name'." );
 116                 }
 117
 118                 return $this->procCache['config'][$name];
 119         }
 120
 121         /**
 122          * @throws ConfigException
 123          */
 124         private function load() {
 125                 if ( $this->procCache !== null ) {
 126                         return; // already loaded
 127                 }
 128
 129                 $now = microtime( true );
 130                 $key = $this->srvCache->makeGlobalKey(
 131                         __CLASS__,
 132                         $this->host,
 133                         $this->directory
 134                 );
 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                         $servers = $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, "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 }