Fix reporting of system.process.cgroup.memory.mem.limit.bytes when limit not set

[AlexanderWert]

Description

The UI team currently does a fairly complex calculation to calculate the total memory usage - the complexity here is added again by memory related metrics based on cgroup. The key issue is in percentCgroupMemoryUsedScript - the system.process.cgroup.memory.mem.limit.bytes may not be set, which means a pod can take up all the memory of the host. But in this case agents typically send the "magic value" of 9223372036854771712L, which is then "fixed" by the UI. While this works for our UI, for a user it's almost impossible to recreate a correct memory usage graph when an APM Agent sends memory related metrics based on cgroups.

Solution

Decrease the complexity of the UI codeI by sending "real" system.process.cgroup.memory.mem.limit.bytes. This means, if no memory limit is set for the POD, the agent won't send the "magic" 9223372036854771712L value, instead, it'll send system.memory.total in system.process.cgroup.memory.mem.limit.bytes. This means the max memory that a pod can take is the same as the overall system memory.

Spec Issue

• [META 811] Spec: Fix reporting of system.process.cgroup.memory.mem.limit.bytes when limit not set #812

Agent Issues

• [META 811] Fix reporting of system.process.cgroup.memory.mem.limit.bytes when limit not set apm-agent-java#3210
• [META 811] Fix reporting of system.process.cgroup.memory.mem.limit.bytes when limit not set apm-agent-dotnet#2123
• [META 811] Fix reporting of system.process.cgroup.memory.mem.limit.bytes when limit not set apm-agent-nodejs#3450
• [META 811] Fix reporting of system.process.cgroup.memory.mem.limit.bytes when limit not set apm-agent-python#1865

[gregkalapos]

Duplicate of #814