prometheus support & shell scripts integration with netdata

[ktsaou]

prometheus

fixes #1497

Prometheus is polling for data. This PR adds a new API method to netdata /api/v1/allmetrics?format=prometheus.

This call returns the latest collected values for all metrics collected by netdata.

shell

Now shell scripts can run:

eval "$(curl -s 'http://localhost:19999/api/v1/allmetrics')"

after this command, all the netdata metrics are exposed to shell. Check:

# source the metrics
eval "$(curl -s 'http://localhost:19999/api/v1/allmetrics')"

# let's see if there are variables exposed by netdata for system.cpu
set | grep "^NETDATA_SYSTEM_CPU"

NETDATA_SYSTEM_CPU_GUEST=0
NETDATA_SYSTEM_CPU_GUEST_NICE=0
NETDATA_SYSTEM_CPU_IDLE=95
NETDATA_SYSTEM_CPU_IOWAIT=0
NETDATA_SYSTEM_CPU_IRQ=0
NETDATA_SYSTEM_CPU_NICE=0
NETDATA_SYSTEM_CPU_SOFTIRQ=0
NETDATA_SYSTEM_CPU_STEAL=0
NETDATA_SYSTEM_CPU_SYSTEM=1
NETDATA_SYSTEM_CPU_USER=4
NETDATA_SYSTEM_CPU_VISIBLETOTAL=5

# let's see the total cpu utilization of the system
echo ${NETDATA_SYSTEM_CPU_VISIBLETOTAL}
5

# what about alarms?
set | grep "^NETDATA_ALARM_SYSTEM_SWAP_"
NETDATA_ALARM_SYSTEM_SWAP_RAM_IN_SWAP_STATUS=CRITICAL
NETDATA_ALARM_SYSTEM_SWAP_RAM_IN_SWAP_VALUE=53
NETDATA_ALARM_SYSTEM_SWAP_USED_SWAP_STATUS=CLEAR
NETDATA_ALARM_SYSTEM_SWAP_USED_SWAP_VALUE=51

# let's get the current status of the alarm 'ram in swap'
echo ${NETDATA_ALARM_SYSTEM_SWAP_RAM_IN_SWAP_STATUS}
CRITICAL

# is it fast?
time curl -s 'http://localhost:19999/api/v1/allmetrics' >/dev/null

real	0m0,070s
user	0m0,000s
sys	0m0,007s

# it is... 0.07 seconds for curl to be loaded, connect to netdata and fetch the response back...

The _VISIBLETOTAL variable sums up all the dimensions of each chart.

The format of the variables is:

NETDATA_${chart_id^^}_${dimension_id^^}="${value}"

The value is rounded to the closest integer, since shell script cannot process decimal numbers.