Amazon Web Services (AWS)

AWS環境でのNetScalerを考える

システムの耐障害性を検討する上でネットワーク機器の高可用性は必要不可欠です。このブログでは、AWS環境におけるNetScalerの冗長性を考えます。

始めにオンプレミス環境のNetScalerでは、2台のNetScalerでプライマリ/セカンダリの関係を確立するHigh Availability(以降HA)と、複数台のNetScalerをグルーピングしてトラフィックを捌くCluster、この2つの機能を使用することができます。シンプルにプライマリ/セカンダリで動くHAの方が馴染みあるかと思います。AWS環境においては、NetScalerのClusterがサポートされていません。また、HAも一部制約があり、オンプレミス環境同様に構成することができません。本稿では、AWS環境上でNetScalerの冗長構成を取るにはどのように構成したら良いか説明します。

NetScalerのHAは仮想IPアドレスをプライマリ/セカンダリで共有し、HAフェイルオーバーが発生した際にはGARPを使用することが一般的で、IPとMACアドレスのバインディングの更新を他のネットワークデバイスに通知します。

しかしながらここでまた制限があります。AWS環境ではGARPがサポートされていません。(AWS環境でNetScalerをご利用いただく際の制限はこちらです)

したがって、AWS環境でのNetScalerのHAの考え方はオンプレミス環境での動作の考え方/必要要件とは異なります。AWS環境の機能をうまく利用した別のARPテーブルの更新手段が必要です。

では、HAフェイルオーバー発生時にAWS環境でどのような処理が必要か下図をベースに説明していきます。
例としてAWS環境に構築されたCitrix Virtual Apps and Desktopsへの入り口として、NetScaler(Gateway)が動いています。オンプレミス環境のユーザーからのアクセスがTransit Gatewayを通過しAWSのVPCに到達、NetScaler#1がトラフィックを処理していて、HA切り替わりが発生する前の状態です。

Figure 1

次に、HAフェイルオーバーが発生します。

Figure 2

①NetScaler HAフェイルオーバーが発生

②NetScalerが以下のFQDNをDNSサーバーに名前解決

・ec2.ap-northeast-1.amazonaws.com(東京リージョンの場合)

・iam.amazonaws.com

③NetScalerに付与されたIAM権限をもってNetScalerがAWSコンソール(EC2、IAM)にアクセス

④NetScaler#1を指していた該当のルートをNetScalerが書き換える

Before: 宛先 Nexthop

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