tencent cloud

alarm

Using a single CVM instance as the public gateway has the risk of single point of failure. You are advised to use a NAT gateway in the production environment.

As of December 6, 2019, Tencent Cloud no longer supports configuring a CVM as the public gateway on the CVM purchase page. If you need to configure a gateway, follow the instructions below.

Overview

You can access the internet by using a public gateway CVM with a public IP or EIP when some of your VPC-based CVMs lack the public IPs. The public gateway CVM translates the source IP for outbound traffic. When other CVMs access the internet through the public gateway CVM, the source IPs will be translated into public IP of the public gateway CVM. See the figure below.

Prerequisites

• You are logged in to the CVM console.
• The public gateway CVM and the CVMs that need to access the internet through the public gateway CVM must be in different subnets because the public gateway CVM can only forward requests from other subnets.
• The public gateway CVM must be a Linux CVM. Windows CVMs will not work.

Directions

Step 1: bind an EIP (optional)

Note

Skip this step if the public gateway CVM already has a public IP.

1. Log in to the CVM console and choose EIP on the left sidebar.
2. Locate the EIP to bind the instance, select More > Bind in the Operation column.
   
3. In the pop-up window, select a CVM to be configured and bind it to the EIP.
   

Step 2: configure a route table for the gateway subnet

Note

The gateway subnet and other subnets cannot share the same route table. You need to create a separate route table for the gateway subnet.

1. Create a custom route table.
2. Associate the route table with the subnet where the public gateway CVM resides.
   

Step 3: configure a route table for the other subnets

This route table directs all traffic from the CVMs without a public IP to the public gateway so these CVMs can access public networks as well.
Add the following routing policies to the route table:

• Destination: the public IP you want to access.
• Next hop type: CVM.
• Next hop: private IP of the CVM instance to which the EIP is bound in Step 1.
  For more information, see Manage Route table.
  

Step 4: configure the public gateway

1. Log in to the public gateway CVM instance and perform the following operations to enable the network forwarding and NAT proxy features:

2. Run the following command to create the vpcGateway.sh script in usr/local/sbin.

   vim /usr/local/sbin/vpcGateway.sh
   

3. Press i to switch to the edit mode and add the following code to the script.

   #!/bin/bash
   echo "----------------------------------------------------"
   echo " `date`"
   echo "(1)ip_forward config......"
   file="/etc/sysctl.conf"
   grep -i "^net\.ipv4\.ip_forward.*" $file &>/dev/null && sed -i \
   's/net\.ipv4\.ip_forward.*/net\.ipv4\.ip_forward = 1/' $file || \
   echo "net.ipv4.ip_forward = 1" >> $file
   echo 1 >/proc/sys/net/ipv4/ip_forward
   [ `cat /proc/sys/net/ipv4/ip_forward` -eq 1 ] && echo "-->ip_forward:Success" || \
   echo "-->ip_forward:Fail"
   echo "(2)Iptables set......"
   iptables -t nat -A POSTROUTING -j MASQUERADE && echo "-->nat:Success" || echo "-->nat:Fail"
   iptables -t mangle -A POSTROUTING -p tcp -j TCPOPTSTRIP --strip-options timestamp && \
   echo "-->mangle:Success" || echo "-->mangle:Fail"
   echo "(3)nf_conntrack config......"
   echo 262144 > /sys/module/nf_conntrack/parameters/hashsize
   [ `cat /sys/module/nf_conntrack/parameters/hashsize` -eq 262144 ] && \
   echo "-->hashsize:Success" || echo "-->hashsize:Fail"
   echo 1048576 > /proc/sys/net/netfilter/nf_conntrack_max
   [ `cat /proc/sys/net/netfilter/nf_conntrack_max` -eq 1048576 ] && \
   echo "-->nf_conntrack_max:Success" || echo "-->nf_conntrack_max:Fail"
   echo 10800 >/proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established \
   [ `cat /proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established` -eq 10800 ] \
   && echo "-->nf_conntrack_tcp_timeout_established:Success" || \
   echo "-->nf_conntrack_tcp_timeout_established:Fail"
   

4. Click Esc and enter :wq to save and close the file.

5. Run the following command to set the script permission.

   chmod +x /usr/local/sbin/vpcGateway.sh
   echo "/usr/local/sbin/vpcGateway.sh >/tmp/vpcGateway.log 2>&1" >> /etc/rc.local
   

6. Set the RPS of the public gateway.

7. Run the following command to create the set_rps.sh script in usr/local/sbin.

   vim /usr/local/sbin/set_rps.sh
   

8. Press i to switch to the edit mode and add the following code to the script.

   # !/bin/bash
   echo "--------------------------------------------"
   date
   mask=0
   i=0
   total_nic_queues=0
   get_all_mask() {
   local cpu_nums=$1
   if [ $cpu_nums -gt 32 ]; then
   mask_tail=""
   mask_low32="ffffffff"
   idx=$((cpu_nums / 32))
   cpu_reset=$((cpu_nums - idx * 32))
   if [ $cpu_reset -eq 0 ]; then
   mask=$mask_low32
   for ((i = 2; i <= idx; i++)); do
   mask="$mask,$mask_low32"
   done
   else
   for ((i = 1; i <= idx; i++)); do
   mask_tail="$mask_tail,$mask_low32"
   done
   mask_head_num=$((2 ** cpu_reset - 1))
   mask=$(printf "%x%s" $mask_head_num $mask_tail)
   fi
   else
   mask_num=$((2 ** cpu_nums - 1))
   mask=$(printf "%x" $mask_num)
   fi
   echo $mask
   }
   set_rps() {
   if ! command -v ethtool &>/dev/null; then
   source /etc/profile
   fi
   ethtool=$(which ethtool)
   cpu_nums=$(cat /proc/cpuinfo | grep processor | wc -l)
   if [ $cpu_nums -eq 0 ]; then
   exit 0
   fi
   mask=$(get_all_mask $cpu_nums)
   echo "cpu number:$cpu_nums mask:0x$mask"
   ethSet=$(ls -d /sys/class/net/eth*)
   for entry in $ethSet; do
   eth=$(basename $entry)
   nic_queues=$(ls -l /sys/class/net/$eth/queues/ | grep rx- | wc -l)
   if (($nic_queues == 0)); then
   continue
   fi
   cat /proc/interrupts | grep "LiquidIO.*rxtx" &>/dev/null
   if [ $? -ne 0 ]; then # not smartnic
   #multi queue don't set rps
   max_combined=$(
   $ethtool -l $eth 2>/dev/null | grep -i "combined" | head -n 1 | awk '{print $2}'
   )
   #if ethtool -l $eth goes wrong.
   [[ ! "$max_combined" =~ ^[0-9]+$ ]] && max_combined=1
   if [ ${max_combined} -ge ${cpu_nums} ]; then
   echo "$eth has equally nic queue as cpu, don't set rps for it..."
   continue
   fi
   else
   echo "$eth is smartnic, set rps for it..."
   fi
   echo "eth:$eth queues:$nic_queues"
   total_nic_queues=$(($total_nic_queues + $nic_queues))
   i=0
   while (($i < $nic_queues)); do
   echo $mask >/sys/class/net/$eth/queues/rx-$i/rps_cpus
   echo 4096 >/sys/class/net/$eth/queues/rx-$i/rps_flow_cnt
   i=$(($i + 1))
   done
   done
   flow_entries=$((total_nic_queues * 4096))
   echo "total_nic_queues:$total_nic_queues flow_entries:$flow_entries"
   echo $flow_entries >/proc/sys/net/core/rps_sock_flow_entries
   }
   set_rps
   

9. Click Esc and enter :wq to save and close the file.

10. Run the following command to set the script permission.

    chmod +x /usr/local/sbin/set_rps.sh
    echo "/usr/local/sbin/set_rps.sh >/tmp/setRps.log 2>&1" >> /etc/rc.local
    chmod +x /etc/rc.d/rc.local
    

11. Restart the public gateway CVM to apply the configurations. Then, test if a CVM without a public IP can access the Internet through the public gateway CVM.