netdata/health

Health monitoring

Each netdata node runs an independent thread evaluating health monitoring checks. This thread has lock free access to the database, so that it can operate as a watchdog.

Health checks (alarms) are attached to netdata charts, allowing netdata to automatically activate an alarm as soon as a chart is created. This is very important for netdata, since many charts are dynamically created during runtime (for example, the chart tracking network interface packet drops, is automatically created on the first packet dropped).

Netdata also supports alarm templates, so that an alarm can be attached to all the charts of the same context (i.e. all network interfaces, or all disks, or all mysql servers, etc.)

Each alarm can execute a single query to the database using statistical algorithms against past data, but alarms can be combined. So, if you need 2 queries in the database, you can combine 2 alarms together (both will run a query to the database, and the results can be combined).

Each alarm has unlimited access to all the metrics collected. So, a single alarm can use expressions combining the latest value of any number of metrics.

Health configuration reference

Stock netdata health configuration is in /usr/lib/netdata/conf.d/health.d. These files can be overwritten by copying them and editing them in /etc/netdata/health.d (run /etc/netdata/edit-config to edit them).

In /etc/netdata/health.d you can also put any number of files (in any number of sub-directories) with a suffix .conf to have them processed by netdata.

Health configuration can be reloaded at any time, without restarting netdata. Just send netdata the SIGUSR2 signal, like this:

killall -USR2 netdata

Entities in the health files

There are 2 entities:

1. alarms, which are attached to specific charts, and

2. templates, which define rules that should be applied to all charts having a specific context. You can use this feature to apply alarms to all disks, all network interfaces, all mysql databases, all nginx web servers, etc.

Both of these entities have exactly the same format and feature set. The only difference is the label alarm or template.

Netdata supports overriding templates with alarms. For example, when a template is defined for a set of charts, an alarm with exactly the same name attached to the same chart the template matches, will have higher precedence (i.e. netdata will use the alarm on this chart and prevent the template from being applied to it).

The format

The following lines are parsed.

Alarm line alarm or template

This line starts an alarm or alarm template.

alarm: NAME

or

template: NAME

This line has to be first on each alarm or template. NAME is anything you would like to name it (the only symbols allowed are . and _).

---

Alarm line on

This line defines the data the alarm should be attached to.

For alarms:

on: CHART

For CHART you can use a chart id or name of the chart, as shown on the dashboard.

For alarm templates:

on: CONTEXT

CONTEXT is the template of a chart. For example the charts mysql_local.net and mysql_server2.net have the same context: mysql.net. So, you can use this to apply alarms to all mysql.net charts.

To find the CONTEXT of a chart hover over its date, above the legend. A tooltip will appear with this format plugin:nodule, context. For example, the bandwidth chart of a network interface says:

proc:/proc/dev/dev, net.net

So, plugin = proc, module = /proc/net/dev and context = net.net.

---

Alarm line os

This alarm or template will be used only if the O/S of the host loading it, matches this pattern list. The value is a space separated list of simple patterns (use * as wildcard, prefix with ! for a negative match, order is important).

os: linux freebsd macos

---

Alarm line hosts

This alarm or template will be used only if the hostname of the host loading it, matches this pattern list. The value is a space separated list of simple patterns (use * as wildcard, prefix with ! for a negative match, order is important).

hosts: server1 server2 database* !redis3 redis*

The above says: use this alarm on all hosts named server1, server2, database*, and all redis* except redis3.

This is useful when you centralize metrics from multiple hosts, to one netdata.

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Alarm line families

This line is only used in alarm templates. It filters the charts. So, if you need to create an alarm template for a few of a kind of chart (a few of your disks, or a few of your network interfaces, or a few your mysql servers, etc), you can create an alarm template that would normally be applied to all of them, and filter them by family.

The format is:

families: SIMPLE PATTERN LIST

Simple patterns list is a lists of space separated patterns. Use * as wildcard and ! for a negative match. Processing is left to right, and on the first hit (positive or negative), processing stops.

So. families: * means, match anything, while families: !bad*pattern* * means anything except bad*pattern* (where * is a wildcard to match any sequence of characters).

The family of a chart is usually the submenu of the netdata dashboard it appears.

---

Alarm line lookup

This lines makes a database lookup to find a value. This result of this lookup is available as $this.

The format is:

lookup: METHOD AFTER [at BEFORE] [every DURATION] [OPTIONS] [of DIMENSIONS]

Everything is the same with badges. In short:

• METHOD is one of average, min, max, sum, incremental-sum. This is required.

• AFTER is a relative number of seconds, but it also accepts a single letter for changing the units, like -1s = 1 second in the past, -1m = 1 minute in the past, -1h = 1 hour in the past, -1d = 1 day in the past. You need a negative number (i.e. how far in the past to look for the value). This is required.

• at BEFORE is by default 0 and is not required. Using this you can define the end of the lookup. So data will be evaluated between AFTER and BEFORE.

• every DURATION sets the updated frequency of the lookup (supports single letter units as above too).

• OPTIONS is a space separated list of percentage, absolute, min2max, unaligned, match-ids, match-names. Check the badges documentation for more info.

• of DIMENSIONS is optional and has to be the last parameter. Dimensions have to be separated by , or |. The space characters found in dimensions will be kept as-is (a few dimensions have spaces in their names). This accepts netdata simple patterns and the match-ids and match-names options affect the searches for dimensions.

The result of the lookup will be available as $this and $NAME in expressions. The timestamps of the timeframe evaluated by the database lookup is available as variables $after and $before (both are unix timestamps).

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Alarm line calc

This expression is evaluated just after the lookup (if any). Its purpose is to apply some calculation before using the value looked up from the db.

You can also have an expression without a lookup, using other variables that are available.

The result of the calculation will be available as $this in warning and critical expressions (overwriting the lookup one).

Format:

calc: EXPRESSION

Check Expressions for more information.

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Alarm line every

Sets the update frequency of this alarm. This is the same to the every DURATION given in the lookup lines.

Format:

every: DURATION

DURATION accepts s for seconds, m is minutes, h for hours, d for days.

---

Alarm lines green and red

Set the green and red thresholds of a chart. Both are available as $green and $red in expressions. If multiple alarms define different thresholds, the ones defined by the first alarm will be used. These will eventually visualized on the dashboard, so only one set of them is allowed. If you need multiple sets of them in different alarms, use absolute numbers instead of $red and $green.

Format:

green: NUMBER
red: NUMBER

---

Alarm lines warn and crit

These expressions should evaluate to true or false (alternatively non-zero or zero). They trigger the alarm. Both are optional.

Format:

warn: EXPRESSION
crit: EXPRESSION

Check Expressions for more information.

---

Alarm line to

This will be the first parameter of the script to be executed when the alarm switches status. Its meaning is left up to the exec script.

The default exec script, alarm-notify.sh, uses this field as a space separated list of roles, which are then consulted to find the exact recipients per notification method.

Format:

to: ROLE1 ROLE2 ROLE3 ...

---

Alarm line exec

The script that will be executed when the alarm changes status.

Format:

exec: SCRIPT

The default SCRIPT is netdata's alarm-notify.sh, which supports all the notifications methods netdata supports, including custom hooks.

---

Alarm line delay

This is used to provide optional hysteresis settings for the notifications, to defend against notification floods. These settings do not affect the actual alarm - only the time the exec script is executed.

Format:

delay: [[[up U] [down D] multiplier M] max X]

• up U defines the delay to be applied to a notification for an alarm that raised its status (i.e. CLEAR to WARNING, CLEAR to CRITICAL, WARNING to CRITICAL). For example, up 10s, the notification for this event will be sent 10 seconds after the actual event. This is used in hope the alarm will get back to its previous state within the duration given. The default U is zero.

• down D defines the delay to be applied to a notification for an alarm that moves to lower state (i.e. CRITICAL to WARNING, CRITICAL to CLEAR, WARNING to CLEAR). For example, down 1m will delay the notification by 1 minute. This is used to prevent notifications for flapping alarms. The default D is zero.

• mutliplier M multiplies U and D when an alarm changes state, while a notification is delayed. The default multiplier is 1.0.

• max X defines the maximum absolute notification delay an alarm may get. The default X is max(U * M, D * M) (i.e. the max duration of U or D multiplied once with M).

Example:

delay: up 10s down 15m multiplier 2 max 1h

The time is 00:00:00 and the status of the alarm is CLEAR.

time of event	new status	delay	notification will be sent	why
00:00:01	WARNING	up 10s	00:00:11	first state switch
00:00:05	CLEAR	down 15m x2	00:30:05	the alarm changes state while a notification is delayed, so it was multiplied
00:00:06	WARNING	up 10s x2 x2	00:00:26	multiplied twice
00:00:07	CLEAR	down 15m x2 x2 x2	00:45:07	multiplied 3 times.

So:

• U and D are multiplied by M every time the alarm changes state (any state, not just their matching one) and a delay is in place.
• All are reset to their defaults when the alarm switches state without a delay in place.

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Expressions

netdata has an internal infix expression parser. This parses expressions and creates an internal structure that allows fast execution of them.

These operators are supported +, -, *, /, <, <=, <>, !=, >, >=, &&, ||, !, AND, OR, NOT. Boolean operators result in either 1 (true) or 0 (false).

The conditional evaluation operator ? is supported too. Using this operator IF-THEN-ELSE conditional statements can be specified. The format is: (condition) ? (true expression) : (false expression). So, netdata will first evaluate the condition and based on the result will either evaluate true expression or false expression. Example: ($this > 0) ? ($avail * 2) : ($used / 2). Nested such expressions are also supported (i.e. true expression and false expression can contain conditional evaluations).

Expressions also support the abs() function.

Expressions can have variables. Variables start with $. Check below for more information.

There are two special values you can use:

• nan, for example $this != nan will check if the variable this is available. A variable can be nan if the database lookup failed. All calculations (i.e. addition, multiplication, etc) with a nan result in a nan.

• inf, for example $this != inf will check if this is not infinite. A value or variable can be infinite if divided by zero. All calculations (i.e. addition, multiplication, etc) with a inf result in a inf.

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Special use of the conditional operator

A common (but not necessarily obvious) use of the conditional evaluation operator is to provide hysteresis around the critical or warning thresholds. This usage helps to avoid bogus messages resulting from small variations in the value when it is varying regularly but staying close to the threshold value, without needing to delay sending messages at all.

An example of such usage from the default CPU usage alarms bundled with netdata is:

warn: $this > (($status >= $WARNING)  ? (75) : (85))
crit: $this > (($status == $CRITICAL) ? (85) : (95))

The above say:

• If the alarm is currently a warning, then the threshold for being considered a warning is 75, otherwise it's 85.

• If the alarm is currently critical, then the threshold for being considered critical is 85, otherwise it's 95.

Which in turn, results in the following behavior:

• While the value is rising, it will trigger a warning when it exceeds 85, and a critical alert when it exceeds 95.

• While the value is falling, it will return to a warning state when it goes below 85, and a normal state when it goes below 75.

• If the value is constantly varying between 80 and 90, then it will trigger a warning the first time it goes above 85, but will remain a warning until it goes below 75 (or goes above 85).

• If the value is constantly varying between 90 and 100, then it will trigger a critical alert the first time it goes above 95, but will remain a critical alert goes below 85 (at which point it will return to being a warning).

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Variables

netdata supports 3 new internal indexes for variables that will be used in health monitoring:

• chart local variables. All the dimensions of the chart are exposed as local variables. All chart alarms names are exposed as variables too.

  Charts also define a few special variables:

  • $last_collected_t is the unix timestamp of the last data collection
  • $collected_total_raw is the sum of all the dimensions (their last collected values)
  • $update_every is the update frequency of the chart
  • $green and $red the threshold defined in alarms (these are per chart - the charts inherits them from the the first alarm that defined them)

  Chart dimensions define their last calculated (i.e. interpolated) value, exactly as shown on the charts, but also a variable with their name and suffix _raw that resolves to the last collected value - as collected and another with suffix _last_collected_t that resolves to unix timestamp the dimension was last collected (there may be dimensions that fail to be collected while others continue normally).

• family variables. Families are used to group charts together. For example all eth0 charts, have family = eth0. This index includes all local variables, but if there are overlapping variables, only the first are exposed.

• host variables. All the dimensions of all charts, including all alarms, in fullname. Fullname is CHART.VARIABLE, where CHART is either the chart id or the chart name (both are supported).

• special variables* are:

  • this, which is resolved to the value of the current alarm.

  • status, which is resolved to the current status of the alarm (the current = the last status, i.e. before the current database lookup and the evaluation of the calc line). This values can be compared with $REMOVED, $UNINITIALIZED, $UNDEFINED, $CLEAR, $WARNING, $CRITICAL. These values are incremental, ie. $status > $CLEAL works as expected.

  • now, which is resolved to current unix timestamp.

You can find all the variables that can be used for a given chart, using http://your.netdata.ip:19999/api/v1/alarm_variables?chart=NAME. This will dump all the indexes from the chart's perspective. Example: variables for the system.cpu chart of the registry.

Alarm Statuses

Alarms can have the following statuses:

• REMOVED - the alarm has been deleted (this happens when a SIGUSR2 is sent to netdata to reload health configuration)

• UNINITIALIZED - the alarm is not initialized yet

• UNDEFINED - the alarm failed to be calculated (i.e. the database lookup failed, a division by zero occurred, etc)

• CLEAR - the alarm is not armed / raised (i.e. is OK)

• WARNING - the warning expression resulted in true or non-zero

• CRITICAL - the critical expression resulted in true or non-zero

The external script will be called for all status changes.

Examples

Check the health/health.d/ directory for all alarms shipped with netdata.

Here are a few examples:

Example 1

A simple check if an apache server is alive:

template: apache_last_collected_secs
      on: apache.requests
    calc: $now - $last_collected_t
   every: 10s
    warn: $this > ( 5 * $update_every)
    crit: $this > (10 * $update_every)

The above checks that netdata is able to collect data from apache. In detail:

template: apache_last_collected_secs

The above defines a template named apache_last_collected_secs. The name is important since $apache_last_collected_secs resolves to the calc line. So, try to give something descriptive.

      on: apache.requests

The above applies the template to all charts that have context = apache.requests (i.e. all your apache servers).

    calc: $now - $last_collected_t

• $now is a standard variable that resolves to the current timestamp.

• $last_collected_t is the last data collection timestamp of the chart. So this calculation gives the number of seconds passed since the last data collection.

  every: 10s
  

The alarm will be evaluated every 10 seconds.

    warn: $this > ( 5 * $update_every)
    crit: $this > (10 * $update_every)

If these result in non-zero or true, they trigger the alarm.

• $this refers to the value of this alarm (i.e. the result of the calc line. We could also use $apache_last_collected_secs.

$update_every is the update frequency of the chart, in seconds.

So, the warning condition checks if we have not collected data from apache for 5 iterations and the critical condition checks for 10 iterations.

Example 2

Check if any of the disks is critically low on disk space:

template: disk_full_percent
      on: disk.space
    calc: $used * 100 / ($avail + $used)
   every: 1m
    warn: $this > 80
    crit: $this > 95

$used and $avail are the used and avail chart dimensions as shown on the dashboard.

So, the calc line finds the percentage of used space. $this resolves to this percentage.

Example 3

Predict if any disk will run out of space in the near future.

We do this in 2 steps:

Calculate the disk fill rate:

    template: disk_fill_rate
          on: disk.space
      lookup: max -1s at -30m unaligned of avail
        calc: ($this - $avail) / (30 * 60)
       every: 15s

In the calc line: $this is the result of the lookup line (i.e. the free space 30 minutes ago) and $avail is the current disk free space. So the calc line will either have a positive number of GB/second if the disk if filling up, or a negative number of GB/second if the disk is freeing up space.

There is no warn or crit lines here. So, this template will just do the calculation and nothing more.

Predict the hours after which the disk will run out of space:

    template: disk_full_after_hours
          on: disk.space
        calc: $avail / $disk_fill_rate / 3600
       every: 10s
        warn: $this > 0 and $this < 48
        crit: $this > 0 and $this < 24

The calc line estimates the time in hours, we will run out of disk space. Of course, only positive values are interesting for this check, so the warning and critical conditions check for positive values and that we have enough free space for 48 and 24 hours respectively.

Once this alarm triggers we will receive an email like this:

Example 4

Check if any network interface is dropping packets:

template: 30min_packet_drops
      on: net.drops
  lookup: sum -30m unaligned absolute
   every: 10s
    crit: $this > 0

The lookup line will calculate the sum of the all dropped packets in the last 30 minutes.

The crit line will issue a critical alarm if even a single packet has been dropped.

Note that the drops chart does not exist if a network interface has never dropped a single packet. When netdata detects a dropped packet, it will add the chart and it will automatically attach this alarm to it.

Troubleshooting

You can compile netdata with debugging and then set in netdata.conf:

[global]
   debug flags = 0x0000000000800000

Then check your /var/log/netdata/debug.log. It will show you how it works. Important: this will generate a lot of output in debug.log.

You can find the context of charts by looking up the chart in either http://your.netdata:19999/netdata.conf or http://your.netdata:19999/api/v1/charts.

You can find how netdata interpreted the expressions by examining the alarm at http://your.netdata:19999/api/v1/alarms?all. For each expression, netdata will return the expression as given in its config file, and the same expression with additional parentheses added to indicate the evaluation flow of the expression.