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/*
* Copyright (c) 2024 Vaughn Nugent
*
* Library: VNLib
* Package: ObjectCacheServer
* File: CacheNodeReplicationMaanger.cs
*
* CacheNodeReplicationMaanger.cs is part of ObjectCacheServer which is part
* of the larger VNLib collection of libraries and utilities.
*
* ObjectCacheServer is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* ObjectCacheServer is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see https://www.gnu.org/licenses/.
*/
using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;
using VNLib.Plugins;
using VNLib.Utils.Logging;
using VNLib.Data.Caching.Extensions;
using static VNLib.Data.Caching.Constants;
using VNLib.Net.Messaging.FBM;
using VNLib.Net.Messaging.FBM.Client;
using VNLib.Plugins.Extensions.Loading;
using VNLib.Data.Caching.Extensions.Clustering;
namespace VNLib.Data.Caching.ObjectCache.Server.Clustering
{
/*
* This class is responsible for replicating the cache with other nodes.
*
* It does this by connecting to other nodes and listening for change events.
* When a change event occurs, it takes action against the local cache store,
* to keep it consistent with the other nodes.
*
* Change events are only handled first-hand, meaning that events do not
* propagate to other nodes, they must be connected individually to each node
* and listen for changes.
*/
internal sealed class CacheNodeReplicationMaanger : IAsyncBackgroundWork
{
private readonly PluginBase _plugin;
private readonly ILogProvider _log;
private readonly FBMClientFactory _clientFactory;
private readonly ObjectCacheSystemState _sysState;
private readonly bool _isDebug;
private int _openConnections;
public CacheNodeReplicationMaanger(PluginBase plugin)
{
_sysState = plugin.GetOrCreateSingleton<ObjectCacheSystemState>();
//Init fbm config with fixed message size
FBMClientConfig clientConfig = FBMDataCacheExtensions.GetDefaultConfig(
_sysState.SharedCacheHeap,
CacheConstants.MaxSyncMessageSize,
debugLog: plugin.IsDebug() ? plugin.Log.CreateScope(CacheConstants.LogScopes.ReplicationFbmDebug) : null
);
//Init ws fallback factory and client factory
_clientFactory = new(
ref clientConfig,
new FBMFallbackClientWsFactory(),
(int)_sysState.ClusterConfig.MaxPeerConnections
);
_plugin = plugin;
_isDebug = plugin.IsDebug();
_log = plugin.Log.CreateScope(CacheConstants.LogScopes.RepliactionManager);
}
public async Task DoWorkAsync(ILogProvider pluginLog, CancellationToken exitToken)
{
_log.Information("Initializing node replication worker");
try
{
while (true)
{
//Get all new peers
CacheNodeAdvertisment[] peers = _sysState.PeerDiscovery.GetNewPeers();
if (peers.Length == 0 && _isDebug)
{
_log.Verbose("No new peers to connect to");
}
//Make sure we don't exceed the max connections
if(_openConnections >= _sysState.ClusterConfig.MaxPeerConnections)
{
if (_isDebug)
{
_log.Verbose("Max peer connections reached, waiting for a connection to close");
}
}
else
{
//Connect to each peer as a background task
foreach (CacheNodeAdvertisment peer in peers)
{
_ = _plugin.ObserveWork(() => OnNewPeerDoWorkAsync(peer, _log, exitToken));
}
}
//Wait for a new peers
await Task.Delay(10000, exitToken);
}
}
catch (OperationCanceledException)
{
//Normal exit
}
catch
{
_log.Error("Node replication worker exited with an error");
throw;
}
finally
{
}
_log.Information("Node replication worker exited");
}
/*
* This method is called when a new peer has connected (or discovered) to establish a
* replication connection.
*/
private async Task OnNewPeerDoWorkAsync(CacheNodeAdvertisment newPeer, ILogProvider log, CancellationToken exitToken)
{
ArgumentNullException.ThrowIfNull(newPeer);
FBMClient client = _clientFactory.CreateClient();
/*
* Notify discovery that we will be listening to this peer
*
* This exists so when a new discovery happens, the work loop will produce
* the difference of new peers to existing peers, and we can connect to them.
* Avoiding infinite connections to the same peer.
*/
_sysState.PeerDiscovery.OnPeerListenerAttached(newPeer);
Interlocked.Increment(ref _openConnections);
try
{
log.Information("Establishing replication connection to peer {server}...", newPeer.NodeId);
//Connect to the server
await client.ConnectToCacheAsync(newPeer, _sysState.NodeConfig, exitToken);
log.Information("Connected to {server}, starting queue listeners", newPeer.NodeId);
//Start worker tasks
List<Task> workerTasks = [];
for (int i = 0; i < Environment.ProcessorCount; i++)
{
Task workerTask = Task.Run(() => ReplicationWorkerDoWorkAsync(client, log, exitToken), exitToken);
workerTasks.Add(workerTask);
}
//Wait for sync workers to exit
await Task.WhenAll(workerTasks);
log.Debug("All cache worker tasks exited successfully, disconnecting from {server}", newPeer.NodeId);
//Disconnect client gracefully
await client.DisconnectAsync(CancellationToken.None);
}
catch(FBMServerNegiationException fbm)
{
log.Error("Failed to negotiate buffer configuration, check your cache memory configuration. Error:{err}", fbm.Message);
}
catch (InvalidResponseException ie)
{
//See if the plugin is unloading
if (!exitToken.IsCancellationRequested)
{
log.Debug("Peer {p} responded with invalid response packet, disconnected. reason\n {reason}", newPeer.NodeId, ie);
}
//Disconnect client gracefully
try
{
await client.DisconnectAsync(CancellationToken.None);
}
catch (Exception ex)
{
log.Error(ex);
}
}
catch (OperationCanceledException)
{
//Plugin unloading, Try to disconnect
try
{
await client.DisconnectAsync(CancellationToken.None);
}
catch (Exception ex)
{
log.Error(ex);
}
}
catch (Exception ex)
{
//Avoid call stacks unless debug or higher logging levels
if (log.IsEnabled(LogLevel.Debug))
{
log.Warn("Lost connection to peer {h}\n {m}", newPeer.NodeId, ex);
}
else
{
log.Warn("Lost connection to peer {h}\n {m}", newPeer.NodeId, ex.Message);
}
}
finally
{
Interlocked.Decrement(ref _openConnections);
client.Dispose();
//Notify monitor of disconnect to make it available again later
_sysState.PeerDiscovery.OnPeerListenerDetatched(newPeer);
}
}
//Wroker task callback method
private async Task ReplicationWorkerDoWorkAsync(FBMClient client, ILogProvider log, CancellationToken exitToken)
{
//Reusable request message
using FBMRequest request = new(in client.Config);
WaitForChangeResult changedObject = new();
//Listen for changes
while (true)
{
//Wait for changes
await client.WaitForChangeAsync(changedObject, exitToken);
log.Debug("Object changed {typ} {obj}", changedObject.Status, changedObject.CurrentId);
switch (changedObject.Status)
{
/*
* During a WFC operation, if a NotFound response is received, it
* means a wait queue was not found for the connection, usually meaning
* the server does not support replication.
*/
case ResponseCodes.NotFound:
log.Error("Server cache not properly configured, worker exiting");
return;
case "deleted":
//Delete the object from the store
await _sysState.InternalStore.DeleteItemAsync(changedObject.CurrentId, CancellationToken.None);
break;
case "modified":
//Reload the record from the store
await UpdateRecordAsync(client, request, log, changedObject.CurrentId, changedObject.NewId, exitToken);
break;
default:
log.Error("Unknown status {status} received from server", changedObject.Status);
break;
}
changedObject.Status = null;
changedObject.CurrentId = null;
changedObject.NewId = null;
//Reset request message
request.Reset();
}
}
private async Task UpdateRecordAsync(FBMClient client, FBMRequest modRequest, ILogProvider log, string objectId, string newId, CancellationToken cancellation)
{
//Set action as get/create
modRequest.WriteHeader(HeaderCommand.Action, Actions.Get);
//Set session-id header
modRequest.WriteHeader(ObjectId, string.IsNullOrWhiteSpace(newId) ? objectId : newId);
//Make request
using FBMResponse response = await client.SendAsync(modRequest, CacheConstants.Delays.CacheSyncGetItemTimeout, cancellation);
response.ThrowIfNotSet();
//Check response code
string status = response.Headers.First(static s => s.Header == HeaderCommand.Status).Value.ToString();
if (ResponseCodes.Okay.Equals(status, StringComparison.Ordinal))
{
//Update the record
await _sysState.InternalStore.AddOrUpdateBlobAsync(objectId, newId, static (t) => t.ResponseBody, response, cancellation);
log.Debug("Updated object {id}", objectId);
}
else
{
log.Warn("Object {id} was missing on the remote server", objectId);
}
}
}
}
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