[Nexthop][fboss2-dev] Add a "fboss2 config rollback" command.

cmake/CliFboss2.cmake

@@ -575,6 +575,8 @@ add_library(fboss2_config_lib
   fboss/cli/fboss2/commands/config/CmdConfigAppliedInfo.cpp
   fboss/cli/fboss2/commands/config/CmdConfigReload.h
   fboss/cli/fboss2/commands/config/CmdConfigReload.cpp
+  fboss/cli/fboss2/commands/config/rollback/CmdConfigRollback.h
+  fboss/cli/fboss2/commands/config/rollback/CmdConfigRollback.cpp
   fboss/cli/fboss2/commands/config/session/CmdConfigSessionCommit.h
   fboss/cli/fboss2/commands/config/session/CmdConfigSessionCommit.cpp
   fboss/cli/fboss2/commands/config/session/CmdConfigSessionDiff.h

fboss/cli/fboss2/BUCK

@@ -771,13 +771,15 @@ cpp_library(
         "CmdListConfig.cpp",
         "commands/config/CmdConfigAppliedInfo.cpp",
         "commands/config/CmdConfigReload.cpp",
+        "commands/config/rollback/CmdConfigRollback.cpp",
         "commands/config/session/CmdConfigSessionCommit.cpp",
         "commands/config/session/CmdConfigSessionDiff.cpp",
         "session/ConfigSession.cpp",
     ],
     headers = [
         "commands/config/CmdConfigAppliedInfo.h",
         "commands/config/CmdConfigReload.h",
+        "commands/config/rollback/CmdConfigRollback.h",
         "commands/config/session/CmdConfigSessionCommit.h",
         "commands/config/session/CmdConfigSessionDiff.h",
         "session/ConfigSession.h",

fboss/cli/fboss2/CmdHandlerImplConfig.cpp

@@ -12,6 +12,7 @@
 
 #include "fboss/cli/fboss2/commands/config/CmdConfigAppliedInfo.h"
 #include "fboss/cli/fboss2/commands/config/CmdConfigReload.h"
+#include "fboss/cli/fboss2/commands/config/rollback/CmdConfigRollback.h"
 #include "fboss/cli/fboss2/commands/config/session/CmdConfigSessionCommit.h"
 #include "fboss/cli/fboss2/commands/config/session/CmdConfigSessionDiff.h"
 
@@ -20,6 +21,7 @@ namespace facebook::fboss {
 template void
 CmdHandler<CmdConfigAppliedInfo, CmdConfigAppliedInfoTraits>::run();
 template void CmdHandler<CmdConfigReload, CmdConfigReloadTraits>::run();
+template void CmdHandler<CmdConfigRollback, CmdConfigRollbackTraits>::run();
 template void
 CmdHandler<CmdConfigSessionCommit, CmdConfigSessionCommitTraits>::run();
 template void

fboss/cli/fboss2/CmdListConfig.cpp

@@ -13,6 +13,7 @@
 #include "fboss/cli/fboss2/CmdHandler.h"
 #include "fboss/cli/fboss2/commands/config/CmdConfigAppliedInfo.h"
 #include "fboss/cli/fboss2/commands/config/CmdConfigReload.h"
+#include "fboss/cli/fboss2/commands/config/rollback/CmdConfigRollback.h"
 #include "fboss/cli/fboss2/commands/config/session/CmdConfigSessionCommit.h"
 #include "fboss/cli/fboss2/commands/config/session/CmdConfigSessionDiff.h"
 
@@ -49,6 +50,12 @@ const CommandTree& kConfigCommandTree() {
        "Reload agent configuration",
        commandHandler<CmdConfigReload>,
        argTypeHandler<CmdConfigReloadTraits>},
+
+      {"config",
+       "rollback",
+       "Rollback to a previous config revision",
+       commandHandler<CmdConfigRollback>,
+       argTypeHandler<CmdConfigRollbackTraits>},
   };
   sort(root.begin(), root.end());
   return root;

fboss/cli/fboss2/commands/config/rollback/CmdConfigRollback.cpp

@@ -0,0 +1,57 @@
+/*
+ *  Copyright (c) 2004-present, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ *
+ */
+
+#include "fboss/cli/fboss2/commands/config/rollback/CmdConfigRollback.h"
+#include "fboss/cli/fboss2/session/ConfigSession.h"
+
+namespace facebook::fboss {
+
+CmdConfigRollbackTraits::RetType CmdConfigRollback::queryClient(
+    const HostInfo& hostInfo,
+    const utils::RevisionList& revisions) {
+  auto& session = ConfigSession::getInstance();
+
+  // Validate arguments
+  if (revisions.size() > 1) {
+    throw std::invalid_argument(
+        "Too many arguments. Expected 0 or 1 revision specifier.");
+  }
+
+  if (!revisions.empty() && revisions[0] == "current") {
+    throw std::invalid_argument(
+        "Cannot rollback to 'current'. Please specify a revision number like 'r42'.");
+  }
+
+  try {
+    int newRevision;
+    if (revisions.empty()) {
+      // No revision specified - rollback to previous revision
+      newRevision = session.rollback(hostInfo);
+    } else {
+      // Specific revision specified
+      newRevision = session.rollback(hostInfo, revisions[0]);
+    }
+    if (newRevision) {
+      return "Successfully rolled back to r" + std::to_string(newRevision) +
+          " and config reloaded.";
+    } else {
+      return "Failed to create a new revision after rollback.";
+    }
+  } catch (const std::exception& ex) {
+    throw std::runtime_error(
+        "Failed to rollback config: " + std::string(ex.what()));
+  }
+}
+
+void CmdConfigRollback::printOutput(const RetType& logMsg) {
+  std::cout << logMsg << std::endl;
+}
+
+} // namespace facebook::fboss

fboss/cli/fboss2/commands/config/rollback/CmdConfigRollback.h

@@ -0,0 +1,39 @@
+/*
+ *  Copyright (c) 2004-present, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ *
+ */
+
+#pragma once
+
+#include "fboss/cli/fboss2/CmdHandler.h"
+#include "fboss/cli/fboss2/utils/CmdClientUtils.h"
+#include "fboss/cli/fboss2/utils/CmdUtils.h"
+
+namespace facebook::fboss {
+
+struct CmdConfigRollbackTraits : public WriteCommandTraits {
+  static constexpr utils::ObjectArgTypeId ObjectArgTypeId =
+      utils::ObjectArgTypeId::OBJECT_ARG_TYPE_ID_REVISION_LIST;
+  using ObjectArgType = utils::RevisionList;
+  using RetType = std::string;
+};
+
+class CmdConfigRollback
+    : public CmdHandler<CmdConfigRollback, CmdConfigRollbackTraits> {
+ public:
+  using ObjectArgType = CmdConfigRollbackTraits::ObjectArgType;
+  using RetType = CmdConfigRollbackTraits::RetType;
+
+  RetType queryClient(
+      const HostInfo& hostInfo,
+      const utils::RevisionList& revisions);
+
+  void printOutput(const RetType& logMsg);
+};
+
+} // namespace facebook::fboss

fboss/cli/fboss2/session/ConfigSession.cpp

@@ -167,6 +167,25 @@ void ensureDirectoryExists(const std::string& dirPath) {
   }
 }
 
+/*
+ * Get the current revision number by reading the symlink target.
+ * Returns -1 if unable to determine the current revision.
+ */
+int getCurrentRevisionNumber(const std::string& systemConfigPath) {
+  std::error_code ec;
+
+  if (!fs::is_symlink(systemConfigPath, ec)) {
+    return -1;
+  }
+
+  std::string target = fs::read_symlink(systemConfigPath, ec);
+  if (ec) {
+    return -1;
+  }
+
+  return ConfigSession::extractRevisionNumber(target);
+}
+
 } // anonymous namespace
 
 ConfigSession::ConfigSession() {
@@ -456,4 +475,100 @@ int ConfigSession::commit(const HostInfo& hostInfo) {
   return revision;
 }
 
+int ConfigSession::rollback(const HostInfo& hostInfo) {
+  // Get the current revision number
+  int currentRevision = getCurrentRevisionNumber(systemConfigPath_);
+  if (currentRevision <= 0) {
+    throw std::runtime_error(
+        "Cannot rollback: cannot determine the current revision from " +
+        systemConfigPath_);
+  } else if (currentRevision == 1) {
+    throw std::runtime_error(
+        "Cannot rollback: already at the first revision (r1)");
+  }
+
+  // Rollback to the previous revision
+  std::string targetRevision = "r" + std::to_string(currentRevision - 1);
+  return rollback(hostInfo, targetRevision);
+}
+
+int ConfigSession::rollback(
+    const HostInfo& hostInfo,
+    const std::string& revision) {
+  ensureDirectoryExists(cliConfigDir_);
+
+  // Build the path to the target revision
+  std::string targetConfigPath = cliConfigDir_ + "/agent-" + revision + ".conf";
+
+  // Check if the target revision exists
+  if (!fs::exists(targetConfigPath)) {
+    throw std::runtime_error(
+        "Revision " + revision + " does not exist at " + targetConfigPath);
+  }
+
+  std::error_code ec;
+
+  // Verify that the system config is a symlink
+  if (!fs::is_symlink(systemConfigPath_)) {
+    throw std::runtime_error(
+        systemConfigPath_ + " is not a symlink. Expected it to be a symlink.");
+  }
+
+  // Read the old symlink target in case we need to undo the rollback
+  std::string oldSymlinkTarget = fs::read_symlink(systemConfigPath_, ec);
+  if (ec) {
+    throw std::runtime_error(
+        "Failed to read symlink " + systemConfigPath_ + ": " + ec.message());
+  }
+
+  // First, create a new revision with the same content as the target revision
+  auto [newRevisionPath, newRevision] =
+      createNextRevisionFile(fmt::format("{}/agent", cliConfigDir_));
+
+  // Copy the target config to the new revision file
+  fs::copy_file(
+      targetConfigPath,
+      newRevisionPath,
+      fs::copy_options::overwrite_existing,
+      ec);
+  if (ec) {
+    // Clean up the revision file we created
+    fs::remove(newRevisionPath);
+    throw std::runtime_error(
+        fmt::format(
+            "Failed to create new revision for rollback: {}", ec.message()));
+  }
+
+  // Atomically update the symlink to point to the new revision
+  atomicSymlinkUpdate(systemConfigPath_, newRevisionPath);
+
+  // Reload the config - if this fails, atomically undo the rollback
+  try {
+    auto client =
+        utils::createClient<apache::thrift::Client<facebook::fboss::FbossCtrl>>(
+            hostInfo);
+    client->sync_reloadConfig();
+  } catch (const std::exception& ex) {
+    // Rollback: atomically restore the old symlink
+    try {
+      atomicSymlinkUpdate(systemConfigPath_, oldSymlinkTarget);
+    } catch (const std::exception& rollbackEx) {
+      // If rollback also fails, include both errors in the message
+      throw std::runtime_error(
+          fmt::format(
+              "Failed to reload config: {}. Additionally, failed to rollback the symlink: {}",
+              ex.what(),
+              rollbackEx.what()));
+    }
+    throw std::runtime_error(
+        fmt::format(
+            "Failed to reload config, symlink was rolled back automatically: {}",
+            ex.what()));
+  }
+
+  // Successfully rolled back
+  LOG(INFO) << "Rollback committed as revision r" << newRevision;
+  return newRevision;
+}
+
 } // namespace facebook::fboss

fboss/cli/fboss2/session/ConfigSession.h

@@ -102,6 +102,11 @@ class ConfigSession {
   // successful.
   int commit(const HostInfo& hostInfo);
 
+  // Rollback to a specific revision or to the previous revision
+  // Returns the revision that was rolled back to
+  int rollback(const HostInfo& hostInfo);
+  int rollback(const HostInfo& hostInfo, const std::string& revision);
+
   // Check if a session exists
   bool sessionExists() const;