How Network Synthetic Monitor works
Network Synthetic Monitor is fully managed by Amazon, and doesn't require separate agents on monitored resources. Instead, you specify probes by providing a VPC subnet and on-premises IP addresses.
When you create a monitor in Network Synthetic Monitor for Amazon-hosted resources, Amazon creates and manages the infrastructure in the background that is required to perform round-trip time and packet loss measurements. Because Amazon manages the required configurations, you can scale your monitoring rapidly, without needing to install or uninstall agents within your Amazon infrastructure.
When probes are created, customized elastic network interfaces (ENIs) are created and attached to probe instances and customer subnets. If Network Synthetic Monitor replaces a probe instance, for example, if it becomes unhealthy, Network Synthetic Monitor detaches the ENIs and reattaches them to the probe replacement. This means that ENI IP addresses are not changed after they are created, unless you delete a probe and create a new one for the same source and destination.
Network Synthetic Monitor focuses monitoring on the routes taken by flows from your Amazon-hosted resources instead of broadly monitoring all flows from your Amazon Web Services Region. If your workloads spread across multiple Availability Zones, Network Synthetic Monitor can monitor routes from each of your private subnets.
Network Synthetic Monitor publishes round-trip time and packet loss metrics to your Amazon CloudWatch account, based on the aggregation interval that you set when you create a monitor. You can also use CloudWatch to set individual latency and packet loss thresholds for each monitor. For example, you might create an alarm for a packet loss sensitive workload to notify you if the packet loss average is higher than a static 0.1% threshold. You can also use CloudWatch anomaly detection to alarm on packet loss or latency metrics that are outside your desired ranges.
Availability and performance measurements
Network Synthetic Monitor sends periodic active probes from your Amazon resource to your on-premises destinations. When you create a monitor, you specify the following:
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Aggregation interval: The time, in seconds, that CloudWatch receives the measured results. This will be either every 30 or 60 seconds. The aggregation period you choose for the monitor applies to all probes in that monitor.
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Probe sources (Amazon resources): A source for a probe is a VPC and associated subnets, or just a VPC subnet, in the Regions where your network operates.
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Probe destinations (customer resources): A destination for a probe is the combination of on-premises IP addresses, network protocols, ports, and network packet size.
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Probe protocol: One of the supported protocols, ICMP or TCP. For more information, see Supported communication protocols.
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Port (for TCP): The port that your network uses to connect.
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Packet size (for TCP): The size, in bytes, of each packet transmitted between your Amazon hosted resource and your destination on a single probe. You can specify a different packet size for each probe in a monitor.
A monitor publishes the following metrics:
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Round-trip time: This metric, measured in microseconds, is a measure of performance. It records the time it takes for the probe to be transmitted to the destination IP address and for the associated response to be received. The round-trip time is the average time observed during the aggregation interval.
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Packet loss: This metric measures the percentage of total packets sent and records the number of transmissions that didn't receive an associated response. No response implies that the packets were lost along the network path.
Supported communication protocols
Network Synthetic Monitor supports two protocols for probes: ICMP and TCP.
ICMP-based probes carry ICMP echo requests from your Amazon hosted resources to the destination address, and expect an ICMP echo reply in response. Network Synthetic Monitor uses the information on the ICMP echo request and reply messages to calculate round-trip time and packet loss metrics.
TCP-based probes carry TCP SYN packets from your Amazon hosted resources to the destination address and port, and expect a TCP SYN+ACK packet in response. Network Synthetic Monitor uses the information on the TCP SYN and TCP SYN+ACK messages to calculate round-trip time and packet loss metrics. Network Synthetic Monitor periodically switches source TCP ports to increase network coverage, which increases the probability of detecting packet loss.
Network health indicator for Amazon
Network Synthetic Monitor publishes a network health indicator (NHI) metric that provides information on issues with the Amazon network for paths that include destinations connected through Amazon Direct Connect.
The NHI binary value is based on a statistical measure of the health of the Amazon-controlled network path from the Amazon hosted resource, where the monitor is deployed, to the Direct Connect location. Network Synthetic Monitor uses anomaly detection to calculate availability drops or lower performance along the network paths.
NHI is not accurate for Amazon Direct Connect attachments that use intermediary routing, such as connections that are created using Cloud WAN or that use Amazon Transit Gateway. When you have a hybrid network that includes Amazon Transit Gateway or other intermediary routing segments, do not use the NHI value as an indication of a performance issue.
Note
Each time that you create a new monitor, add a probe, or re-activate a probe, the NHI for the monitor is delayed by a few hours while Amazon collects data to perform anomaly detection.
To provide the NHI value, Network Synthetic Monitor applies statistical correlation across Amazon sample datasets, as well as to the packet loss and round-trip latency metrics for traffic simulating your network path. NHI can be one of two values: 1 or 0. A value of 1 indicates that Network Synthetic Monitor observed a network degradation within the Amazon controlled network path. A value of 0 indicates that Network Synthetic Monitor did not observe any network degradation for the Amazon network along the path. Using the NHI value enables you to more quickly gain awareness of the cause of network issues. For example, you can set alerts on the NHI metric so you're notified about ongoing issues with the Amazon network along your network paths.
Support for IPv4 and IPv6 addresses
Network Synthetic Monitor provides availability and performance metrics over IPv4 or IPv6 networks, and can monitor either IPv4 or IPv6 addresses from dual-stack VPCs. Network Synthetic Monitor doesn’t allow both IPv4 and IPv6 destinations to be configured in the same monitor; you can create separate monitors for IPv4-only and IPv6-only destinations.