Container Instance Memory Management
When the Amazon ECS container agent registers a container instance into a cluster, the agent
must determine how much memory the container instance has available to reserve for your
tasks. Because of platform memory overhead and memory occupied by the system kernel,
this number is different than the installed memory amount that is advertised for Amazon
EC2
instances. For example, an m4.large instance has 8 GiB of installed memory.
However, this does not always translate to exactly 8192 MiB of memory available for
tasks when the container instance registers.
If you specify 8192 MiB for the task, and none of your container instances have 8192 MiB or greater of memory available to satisfy this requirement, then the task cannot be placed in your cluster.
You should also reserve some memory for the Amazon ECS container agent and other critical system processes on your container instances, so that your task's containers do not contend for the same memory and possibly trigger a system failure. For more information, see Reserving System Memory.
The Amazon ECS container agent uses the Docker ReadMemInfo() function to query the
total memory available to the operating system. Both Linux
and Windows provide command line utilities to determine the total memory.
例 - Determine Linux total memory
The free command returns the total memory that is recognized by the operating system.
free -b
Example output for an m4.large instance running the
Amazon ECS-optimized Linux AMI.
total used free shared buffers cached Mem:8373026816348180480 8024846336 90112 25534464 205418496 -/+ buffers/cache: 117227520 8255799296
This instance has 8373026816 bytes of total memory, which translates to 7985 MiB available for tasks.
例 - Determine Windows total memory
The wmic command returns the total memory that is recognized by the operating system.
wmic ComputerSystem get TotalPhysicalMemory
Example output for an m4.large instance running the
Amazon ECS-optimized Windows AMI.
TotalPhysicalMemory8589524992
This instance has 8589524992 bytes of total memory, which translates to 8191 MiB available for tasks.
Reserving System Memory
If you occupy all of the memory on a container instance with your tasks, then it is
possible that your tasks will contend with critical system processes for memory
and possibly trigger a system failure. The Amazon ECS container agent provides a
configuration variable called ECS_RESERVED_MEMORY, which you can use to
remove a specified number of MiB of memory from the pool that is allocated to your
tasks. This effectively reserves that memory for critical system processes.
For example, if you specify ECS_RESERVED_MEMORY=256 in
your container agent configuration file, then the agent registers the total memory
minus
256 MiB for that instance, and 256 MiB of memory could not be allocated by ECS tasks.
For more information about agent configuration variables and how to set them, see
Amazon ECS 容器代理配置 and 使用 Amazon EC2 用户数据引导启动容器实例.
Viewing Container Instance Memory
You can view how much memory a container instance registers with in the Amazon ECS console (or with the DescribeContainerInstances API operation). If you are trying to maximize your resource utilization by providing your tasks as much memory as possible for a particular instance type, you can observe the memory available for that container instance and then assign your tasks that much memory.
To view container instance memory
-
Open the Amazon ECS console at https://console.amazonaws.cn/ecs/.
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Choose the cluster that hosts your container instances to view.
-
Choose ECS Instances, and select a container instance from the Container Instance column to view.
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The Resources section shows the registered and available memory for the container instance.
The Registered memory value is what the container instance registered with Amazon ECS when it was first launched, and the Available memory value is what has not already been allocated to tasks.