v0.9.0-dev started emitting a Terminated event every time a task process
exited. While this wasn't true in previous versions, it's a useful task
event because it's the only place for job operators to view the task's
exit code.
This behavior is asserted in the e2e/taskevents tests.
Track current memory usage, `memory.usage_in_bytes`, in addition to
`memory.max_memory_usage_in_bytes` and friends. This number is closer
what Docker reports.
Related to https://github.com/hashicorp/nomad/issues/5165 .
plugins/driver: update driver interface to support streaming stats
client/tr: use streaming stats api
TODO:
* how to handle errors and closed channel during stats streaming
* prevent tight loop if Stats(ctx) returns an error
drivers: update drivers TaskStats RPC to handle streaming results
executor: better error handling in stats rpc
docker: better control and error handling of stats rpc
driver: allow stats to return a recoverable error
This PR fixes various instances of plugins being launched without using
the parent loggers. This meant that logs would not all go to the same
output, break formatting etc.
This PR improves how killing a task is handled. Before the kill function
directly orchestrated the killing and was only valid while the task was
running. The new behavior is to mark the desired state and wait for the
task runner to converge to that state.
We were just emitting Killed/Terminated events before. In v0.8 we
emitted Killing/Killed, but lacked Terminated when explicitly stopping
a task. This change makes it so Terminated is always included, whether
explicitly stopping a task or it exiting on its own.
New output:
2019-01-04T14:58:51-08:00 Killed Task successfully killed
2019-01-04T14:58:51-08:00 Terminated Exit Code: 130, Signal: 2
2019-01-04T14:58:51-08:00 Killing Sent interrupt
2019-01-04T14:58:51-08:00 Leader Task Dead Leader Task in Group dead
2019-01-04T14:58:49-08:00 Started Task started by client
2019-01-04T14:58:49-08:00 Task Setup Building Task Directory
2019-01-04T14:58:49-08:00 Received Task received by client
Old (v0.8.6) output:
2019-01-04T22:14:54Z Killed Task successfully killed
2019-01-04T22:14:54Z Killing Sent interrupt. Waiting 5s before force killing
2019-01-04T22:14:54Z Leader Task Dead Leader Task in Group dead
2019-01-04T22:14:53Z Started Task started by client
2019-01-04T22:14:53Z Task Setup Building Task Directory
2019-01-04T22:14:53Z Received Task received by client
Simplify allocDir.Build() function to avoid depending on client/structs,
and remove a parameter that's always set to `false`.
The motivation here is to avoid a dependency cycle between
drivers/cstructs and alloc_dir.
**The Bug:**
You may have seen log lines like this when running 0.9.0-dev:
```
... client.alloc_runner.task_runner: some environment variables not available for rendering: ... keys="attr.driver.docker.volumes.enabled, attr.driver.docker.version, attr.driver.docker.bridge_ip, attr.driver.qemu.version"
```
Not only should we not be erroring on builtin driver attributes, but the
results were nondeterministic due to map iteration order!
The root cause is that we have an old root attribute for all drivers
like:
```
attr.driver.docker = "1"
```
When attributes were opaque variable names it was fine to also have
"nested" attributes like:
```
attr.driver.docker.version = "1.2.3"
```
However in the HCLv2 world the variable names are no longer opaque: they
form an object tree. The `docker` object can no longer both hold a value
(`"1"`) *and* nested attributes (`version = "1.2.3"`).
**The Fix:**
Since the old `attr.driver.<name> = "1"` attribues are useless for task
config interpolation, create a new precedence rule for creating the task
config evaluation context:
*Maps take precedence over primitives.*
This means `attr.driver.docker.version` will always take precedence over
`attr.driver.docker`. The results are determinstic and give users access
to the more useful metadata.
I made this a general precedence rule instead of special-casing driver
attrs because it seemed like better default behavior than spamming
WARNings to logs that were likely unactionable by users.
Unfortunately I don't know how to test these errors. As far as I can
tell they should only happen if there was a programming error in the
upgrade code or the underlying boltdb was corrupted somehow.
* Prefix task bucket with task- to prevent name conflicts
* Shorten device manager bucket name
* Remove commented out outdated var
* Update layout comment
The driver manager is modeled after the device manager and is started by the client.
It's responsible for handling driver lifecycle and reattachment state, as well as
processing the incomming fingerprint and task events from each driver. The mananger
exposes a method for registering event handlers for task events that is used by the
task runner to update the server when a task has been updated with an event.
Since driver fingerprinting has been implemented by the driver manager, it is no
longer needed in the fingerprint mananger and has been removed.
The RestartCount is not really suitable for use as a source of
uniqueness within task invocations as it is not monotonic, and interacts
with the restart stanza in a users config, so conflates restarts due to
task failures, with restarts due to enviromental changes, such as consul
template or vault secrets changing.
Here we instead use a substring from a uuid, which is more random than
we strictly need, but is nicer than rolling our own random string
generator here.
This creates a new buffered channel and goroutine on the allocrunner for
serializing updates to allocations. This allows us to take updates off
the routine that is used from processing updates from the server,
without having complicated machinery for tracking update lifetimes, or
other external synchronization.
This results in a nice performance improvement and signficantly better
throughput on batch changes such as preempting a large number of jobs
for a larger placement.
This commit reduces the locking required to shutdown or destroy
allocrunners, and allows parallel shutdown and destroy of allocrunners during
shutdown.
The assertion here is causing many spurious failures that aren't
actually relevant to the test itself.
We are tracking the cause for this failure independently, and it would
make more sense to have a dedicated test for clean shutdown.
Currently, there is a race condition between creating a taskrunner, and
updating node attributes via fingerprinting.
This is because the taskenv builder will try to iterate over the
clientconfig.Node.Attributes map, which can be concurrently updated by
the fingerprinting process, thus causing a panic.
This fixes that by providing a copy of the clientconfg to the
allocrunner inside the Read lock during config creation.
The allocLock is used to synchronize access to the alloc runner map, not
to ensure internal consistency of the alloc runners themselves. This
updates the updateAlloc process to avoid hanging on to an exclusive lock
of the map while applying changes to allocrunners themselves, as they
should be internally consistent.
This fixes a bug where any client allocation api will block during the
shutdown or updating of an allocrunner and its child taskrunners.
Fixes a bug where a driver health and attributes are never updated from
their initial status. If a driver started unhealthy, it may never go
into a healthy status.
Noticed few places where tests seem to block indefinitely and panic
after the test run reaches the test package timeout.
I intend to follow up with the proper fix later, but timing out is much
better than indefinitely blocking.
When starting an allocation that is preempting other allocs, we create a
new group allocation watcher, and then wait for the allocations to
terminate in the allocation PreRun hooks.
If there's no preempted allocations, then we simply provide a
NoopAllocWatcher.
The Group Alloc watcher is an implementation of a PrevAllocWatcher that
can wait for multiple previous allocs before terminating.
This is to be used when running an allocation that is preempting upstream
allocations, and thus only supports being ran with a local alloc watcher.
It also currently requires all of its child watchers to correctly handle
context cancellation. Should this be a problem, it should be fairly easy
to implement a replacement using channels rather than a waitgroup.
It obeys the PrevAllocWatcher interface for convenience, but it may be
better to extract Migration capabilities into a seperate interface for
greater clarity.
As of now, FileRotator uses bufio.Write under the hood to write data to
configured output file. Due to the way how bufio handles any occurred io
error - saves it into `err` variable never resetting it automatically -
any operation like `Write`, `Flush` etc will become a no-op, returning the very same,
saved error (eg. Out of disk space) even when the problem is fixed (eg. disk
space is available again).
That automatically means that FileRotator will stop writing any logs,
reporting the same error over and over again, even if it's no longer
valid.
This PR fixes it by resetting the bufio Writer, which resets any errors
and tries to write requested data.
IOPS have been modelled as a resource since Nomad 0.1 but has never
actually been detected and there is no plan in the short term to add
detection. This is because IOPS is a bit simplistic of a unit to define
the performance requirements from the underlying storage system. In its
current state it adds unnecessary confusion and can be removed without
impacting any users. This PR leaves IOPS defined at the jobspec parsing
level and in the api/ resources since these are the two public uses of
the field. These should be considered deprecated and only exist to allow
users to stop using them during the Nomad 0.9.x release. In the future,
there should be no expectation that the field will exist.
The previous integration test was broken during the client refactor, and
it seems to be some sort of race with state updating.
I'm going to try and construct a replacement test as part of work on
performance, but for now, the underlying behaviour is still being
tested.
This removes a cyclical dependency when importing client/structs from
dependencies of the plugin_loader, specifically, drivers. Due to
client/config also depending on the plugin_loader.
It also better reflects the ownership of fingerprint structs, as they
are fairly internal to the fingerprint manager.
The logging package is used by logmon and the legacy mock_driver. Because the
legacy drivers are going away, I'm moving it here to signify its actual
ownership.
As part of deprecating legacy drivers, we're moving the env package to a
new drivers/shared tree, as it is used by the modern docker and rkt
driver packages, and is useful for 3rd party plugins.
Looking at NewTaskRunner I'm unsure whether TaskRunner.TaskResources
(from which req.TaskResources is set) is intended to be nil at times or
if the TODO in NewTaskRunner is intended to ensure it is always non-nil.
The old approach was incomplete. Hook env vars are now:
* persisted and restored between agent restarts
* deterministic (LWW if 2 hooks set the same key)
This PR introduces a device hook that retrieves the device mount
information for an allocation. It also updates the computed node class
computation to take into account devices.
TODO Fix the task runner unit test. The environment variable is being
lost even though it is being properly set in the prestart hook.
The group utility struct does not support asynchronously launched
goroutines (goroutines-inside-of-goroutines), so switch those uses to a
normal go call.
This means watchNodeUpdates and watchNodeEvents may not be shutdown when
Shutdown() exits. During nomad agent shutdown this does not matter.
During tests this means a test may leak those goroutines or be unable to
know when those goroutines have exited.
Since there's no runtime impact and these goroutines do not affect alloc
state syncing it seems ok to risk leaking them.
We were incorrectly returning a 0 duration to the taskrunner when
determining when a task should restart. This would cause tasks to be
restarted immediately, ignoring the restart {} stanza in a users
configuration.
This commit causes us to return the restart duration to the task runner
so it may correctly delay further execution.
This change makes few compromises:
* Looks up the devices associated with tasks at look up time. Given
that `nomad alloc status` is called rarely generally (compared to stats
telemetry and general job reporting), it seems fine. However, the
lookup overhead grows bounded by number of `tasks x total-host-devices`,
which can be significant.
* `client.Client` performs the task devices->statistics lookup. It
passes self to alloc/task runners so they can look up the device statistics
allocated to them.
* Currently alloc/task runners are responsible for constructing the
entire RPC response for stats
* The alternatives for making task runners device statistics aware
don't seem appealing (e.g. having task runners contain reference to hostStats)
* On the alloc aggregation resource usage, I did a naive merging of task device statistics.
* Personally, I question the value of such aggregation, compared to
costs of struct duplication and bloating the response - but opted to be
consistent in the API.
* With naive concatination, device instances from a single device group used by separate tasks in the alloc, would be aggregated in two separate device group statistics.
In state values, we need to be able to distinguish between zero values
(e.g. `false`) and unset values (e.g. `nil`).
We can alternatively use protobuf `oneOf` and nested map to ensure
consistency of fields that are set together, but the golang
representation does not represent that well and introducing a mismatch
between representations. Thus, I opted not to use it.
Tests expect that as soon as eventer shuts down immediately on context
cancellations; but golang does not guarantee priority when multiple
pending channels are ready in a select statement.
The default job here contains some exec task config (for setting
command and args) that aren't used for mock driver. Now, the alloc
runner seems stricter about validating fields and errors on unexpected
fields.
Updating configs in tests so we can have an explicit task config
whenever driver is set explicitly.
Introduce a device manager that manages the lifecycle of device plugins
on the client. It fingerprints, collects stats, and forwards Reserve
requests to the correct plugin. The manager, also handles device plugins
failing and validates their output.
For lifecycle operations such as Restart and Kill, the client should not
expect driver plugins to be well behaved and close their waitCh on
context cancelation. Always wait on the passed in context as well as the
waitCh.
* Migrated all of the old leader task tests and got them passing
* Refactor and consolidate task killing code in AR to always kill leader
tasks first
* Fixed lots of issues with state restoring
* Fixed deadlock in AR.Destroy if AR.Run had never been called
* Added a new in memory statedb for testing
If ar.state.TaskStates has not been set, set it on the copy of ar.state.
That keeps ar.state manipulations in one location and allows AllocState
to only acquire read-locks.
Although the really exciting change is making WaitForRunning return the
allocations that it started. This should cut down test boilerplate
significantly.
The interesting decision in this commit was to expose AR's state and not
a fully materialized Allocation struct. AR.clientAlloc builds an Alloc
that contains the task state, so I considered simply memoizing and
exposing that method.
However, that would lead to AR having two awkwardly similar methods:
- Alloc() - which returns the server-sent alloc
- ClientAlloc() - which returns the fully materialized client alloc
Since ClientAlloc() could be memoized it would be just as cheap to call
as Alloc(), so why not replace Alloc() entirely?
Replacing Alloc() entirely would require Update() to immediately
materialize the task states on server-sent Allocs as there may have been
local task state changes since the server received an Alloc update.
This quickly becomes difficult to reason about: should Update hooks use
the TaskStates? Are state changes caused by TR Update hooks immediately
reflected in the Alloc? Should AR persist its copy of the Alloc? If so,
are its TaskStates canonical or the TaskStates on TR?
So! Forget that. Let's separate the static Allocation from the dynamic
AR & TR state!
- AR.Alloc() is for static Allocation access (often for the Job)
- AR.AllocState() is for the dynamic AR & TR runtime state (deployment
status, task states, etc).
If code needs to know the status of a task: AllocState()
If code needs to know the names of tasks: Alloc()
It should be very easy for a developer to reason about which method they
should call and what they can do with the return values.
Multiple receivers raced for the WaitResult when killing tasks which
could lead to a deadlock if the "wrong" receiver won.
Wrap handlers in an ugly little proxy to avoid this. At first I wanted
to push this into drivers, but the result is tied to the TR's handle
lifecycle -- not the lifecycle of an alloc or task.
"Ask forgiveness, not permission."
Instead of peaking at TaskStates (which are no longer updated on the
AR.Alloc() view of the world) to only read logs for running tasks, just
try to read the logs and improve the error handling if they don't exist.
This should make log streaming less dependent on AR/TR behavior.
Also fixed a race where the log streamer could exit before reading an
error. This caused no logs or errors to be displayed sometimes when an
error occurred.
Driver plugin framework to facilitate development of driver plugins.
Implementing plugins only need to implement the DriverPlugin interface.
The framework proxies this interface to the go-plugin GRPC interface generated
from the driver.proto spec.
A testing harness is provided to allow implementing drivers to test the full
lifecycle of the driver plugin. An example use:
func TestMyDriver(t *testing.T) {
harness := NewDriverHarness(t, &MyDiverPlugin{})
// The harness implements the DriverPlugin interface and can be used as such
taskHandle, err := harness.StartTask(...)
}
* client/executor: refactor client to remove interpolation
* executor: POC libcontainer based executor
* vendor: use hashicorp libcontainer fork
* vendor: add libcontainer/nsenter dep
* executor: updated executor interface to simplify operations
* executor: implement logging pipe
* logmon: new logmon plugin to manage task logs
* driver/executor: use logmon for log management
* executor: fix tests and windows build
* executor: fix logging key names
* executor: fix test failures
* executor: add config field to toggle between using libcontainer and standard executors
* logmon: use discover utility to discover nomad executable
* executor: only call libcontainer-shim on main in linux
* logmon: use seperate path configs for stdout/stderr fifos
* executor: windows fixes
* executor: created reusable pid stats collection utility that can be used in an executor
* executor: update fifo.Open calls
* executor: fix build
* remove executor from docker driver
* executor: Shutdown func to kill and cleanup executor and its children
* executor: move linux specific universal executor funcs to seperate file
* move logmon initialization to a task runner hook
* client: doc fixes and renaming from code review
* taskrunner: use shared config struct for logmon fifo fields
* taskrunner: logmon only needs to be started once per task
Updated to hclog.
It exposed fields that required an unexported lock to access. Created a
getter methodn instead. Only old allocrunner currently used this
feature.
* vendor: bump libcontainer and docker to remove Sirupsen imports
* vendor: fix bad vendoring of archive package
* vendor: fix api changes to cgroups in executor
* vendor: fix docker api changes
* vendor: update github.com/Azure/go-ansiterm to use non capitalized logrus import
* UpdateState: set state, append event, persist, update servers
* EmitEvent: append event, persist, update servers
* AppendEvent: append event, persist
AppendEvent may not even have to persist, but for the sake of
correctness I'm going with that for now.
* Stopping an alloc is implemented via Updates but update hooks are
*not* run.
* Destroying an alloc is a best effort cleanup.
* AllocRunner destroy hooks implemented.
* Disk migration and blocking on a previous allocation exiting moved to
its own package to avoid cycles. Now only depends on alloc broadcaster
instead of also using a waitch.
* AllocBroadcaster now only drops stale allocations and always keeps the
latest version.
* Made AllocDir safe for concurrent use
Lots of internal contexts that are currently unused. Unsure if they
should be used or removed.
Saves a tiny bit of cpu and some IO. Sadly doesn't prevent all IO on
duplicate writes as the transactions are still created and committed.
$ go test -bench=. -benchmem
goos: linux
goarch: amd64
pkg: github.com/hashicorp/nomad/helper/boltdd
BenchmarkWriteDeduplication_On-4 500 4059591 ns/op 23736 B/op 56 allocs/op
BenchmarkWriteDeduplication_Off-4 300 4115319 ns/op 25942 B/op 55 allocs/op
I think I like this pattern better as some Config vals are mutable
(Alloc) and some aren't and some are used to derive other values and
never used directly.
Promoting them onto the TR struct is a little more work but is hopefully
more clear as to how each value is used.
Tons left to do and lots of churn:
1. No state saving
2. No shutdown or gc
3. Removed AR factory *for now*
4. Made all "Config" structs local to the package they configure
5. Added allocID to GC to avoid a lookup
Really hating how many things use *structs.Allocation. It's not bad
without state saving, but if AllocRunner starts updating its copy things
get racy fast.
In case where gelf/json logging is used, its fairly easy to exceed the 16k limit, resulting in json output being cut up into multiple strings
the result is invalid json lines which can create all kind of badness in the logging server
This fixes https://github.com/hashicorp/nomad/issues/4699
Signed-off-by: Christian Winther <jippignu@gmail.com>
Not setting the host name led the Go HTTP client to expect a certificate
with a DNS-resolvable name. Since Nomad uses `${role}.${region}.nomad`
names ephemeral dir migrations were broken when TLS was enabled.
Added an e2e test to ensure this doesn't break again as it's very
difficult to test and the TLS configuration is very easy to get wrong.
Even when net=none we would attempt to retrieve network information from
rkt which would spew useless log lines such as:
```
testlog.go:30: 20:37:31.409209 [DEBUG] driver.rkt: failed getting network info for pod UUID 8303cfe6-0c10-4288-84f5-cb79ad6dbf1c attempt 2: no networks found. Sleeping for 970ms
```
It would also delay tests for ~60s during the network information retry
period.
So skip this when net=none. It's unlikely anyone actually uses net=none
outside of tests, so I doubt anyone will notice this change.
Official docs:
https://coreos.com/rkt/docs/latest/networking/overview.html#no-loopback-only-networking
It worked, but the old code used a different alloc id for the path than
the actual alloc! Use the same alloc id everywhere to prevent confusing
test output.
Started failing due to the docker redis image switching from Debian
jessie to stretch:
53f8680550 (diff-acff46b161a3b7d6ed01ba79a032acc9)
Switched from Debian based image to Alpine to get a working `ps` command
again (albeit busybox's stripped down implementation)
Sending the Ctrl-Break signal to PowerShell <6 causes it to drop into
debug mode. Closing its output pipe at that point will block
indefinitely and prevent the process from being killed by Nomad.
See the upstream powershell issue for details:
https://github.com/PowerShell/PowerShell/issues/4254
This change removes the addition of the advertise address to the
exported task env vars and instead moves this work into the
NomadFingerprint.Fingerprint which adds this value to the client
attrs. This can then be used within a Nomad job like
${attr.nomad.advertise.address}.
This commit changes the force closing of the stdout/stderr file
descriptor from closing immediately to being closed after a grace
period. This allows the created process to close its own file and allows
copying of the data.
GH #4290
Add digest support to the docker driver image config. This commit
factors out some common code to print the repo:tag (dockerImageRef) for
events/logs as well as parsing the image to retreive the repo,tag
(parseDockerImage) so that the results are consistent/sane for both
repo:tag and repo@sha256:... references.
When pulling an image with a digest, the tag is blank and the repo
contains the digest. See:
https://github.com/fsouza/go-dockerclient/blob/master/image_test.go#L471
We attempt to avoid splitting a log line between two files by detecting
if we are near the file size limit and scanning for new lines and only
flushing those.
BenchmarkRotator/1KB-8 300000 5613 ns/op
BenchmarkRotator/2KB-8 200000 8384 ns/op
BenchmarkRotator/4KB-8 100000 14604 ns/op
BenchmarkRotator/8KB-8 50000 25002 ns/op
BenchmarkRotator/16KB-8 30000 47572 ns/op
BenchmarkRotator/32KB-8 20000 92080 ns/op
BenchmarkRotator/64KB-8 10000 165883 ns/op
BenchmarkRotator/128KB-8 5000 294405 ns/op
BenchmarkRotator/256KB-8 2000 572374 ns/op
Guard against Canary being set to false at the same time as an
allocation is being stopped: this could cause RemoveTask to be called
with the wrong Canary value and leaking a service.
Deleting both Canary values is the safest route.
Also refactor Consul ServiceClient to take a struct instead of a massive
set of arguments. Meant updating a lot of code but it should be far
easier to extend in the future as you will only need to update a single
struct instead of every single call site.
Adds an e2e test for canary tags.
If two jobs are pulling the same image simultaneously, which ever starts the pull first will set the pull timeout.
This can lead to a poor UX where the first job requested a short timeout while the second job requested a longer timeout
causing the pull to potentially timeout much sooner than expected by the second job.
In the old code `sending` in the `send()` method shared the Data slice's
underlying backing array with its caller. Clearing StreamFrame.Data
didn't break the reference from the sent frame to the StreamFramer's
data slice.
According to go/codec's docs, Reset(...) should be called on
Decoders/Encoders before reuse:
https://godoc.org/github.com/ugorji/go/codec
I could find no evidence that *not* calling Reset() caused bugs, but
might as well do what the docs say?
Remove the NOMAD_TEST_RKT flag as a guard for rkt tests. Still require
Linux, root, and rkt to be installed. Only check for rkt installation
once in hopes of speeding up rkt tests a bit.
Adding this fields to the DriverContext object, will allow us to pass
them to the drivers.
An use case for this, will be to emit tagged metrics in the drivers,
which contain all relevant information:
- Job
- TaskGroup
- Task
- ...
Ref: https://github.com/hashicorp/nomad/pull/4185
Having the Nomad executor create parent cgroups that rkt is launched
within allows the stats collection code used for the exec driver to Just
Work. The only downside is that now the Nomad executor's resource
utilization counts against the cgroups resource limits just as it does
for the exec driver.
I could not reproduce the failure locally even with `stress -cpu ...`
eating all the cpu it could on my machine.
But I think the race was in one of two places:
* The task could restart which could create new events
* I think there could be a race between the updater's version of events
and alloc runners as updates are async
I fixed both. Here's hoping that fixes this flaky test.
This PR does:
1. Health message based on detection has format "Driver XXX detected"
and "Driver XXX not detected"
2. Set initial health description based on detection status and don't
wait for the first health check.
3. Combine updating attributes on the node, fingerprint and health
checking update for drivers into a single call back.
4. Condensed driver info in `node status` only shows detected drivers
and make the output less wide by removing spaces.
Handle the ErrNoLeader case and apply slower retries. Also when we have
missed the heartbeat retry aggressively, backing off after we have
missed for more than 30 seconds.
We were incorrectly relying on the count of alloc updates in a number of
tests. Since alloc updates are async, their number is non-determinstic
and largely meaningless.
This should fix quite a few flaky tests in Travis and prevent future
mistaken assumptions in tests.
We performed the DeploymentStatus nil checks a couple different ways, so
hopefully this helper will consoldiate them and make it more clear what
the code is doing.
When restarts.attempts=0 was set in a jobspec a system or service alloc
that exited with 0 status would be marked as `completed` instead of
`failed`. Since system and service jobs are intended to run until
stopped or updated, they should always be marked as failed when they
exit even in cases where the exit code is 0.
Allow to set the total memory of an agent in its configuration file. This
can be used in case the automatic detection doesn't work or in specific
environments when memory overcommit (using swap for example) can be
desirable.
The interface+mock just to test this one little error handling may seem
like overkill but there was just no other way to write an automated test
around this logic as there's no way to simluate this error with stock
Docker.
Instead of checking Consul's version on startup to see if it supports
TLSSkipVerify, assume that it does and only log in the job service
handler if we discover Consul does not support TLSSkipVerify.
The old code would break TLSSkipVerify support if Nomad started before
Consul (such as on system boot) as TLSSkipVerify would default to false
if Consul wasn't running. Since TLSSkipVerify has been supported since
Consul 0.7.2, it's safe to relax our handling.
A comment in the nomad source code states that swapping for
executor_linux allocations is disabled but it wasn't.
Nomad wrote -1 to the memsw.limit_in_bytes cgroup file to disable
swapping.
This has the following problems:
1.) Writing -1 to the file does not disable swapping. It sets
the limit for memory and swap to unlimited.
2.) On common Linux distributions like Ubuntu 16.04 LTS the
memsw.limit_in_bytes cgroup file does not exist by default.
The memsw.limit_in_bytes file only exist if the Linux kernel is
build with CONFIG_MEMCG_SWAP=yes and either
CONFIG_MEMCG_SWAP_ENABLED=yes or when the kernel parameter
swapaccount=1 is passed during boot.
Most Linux distributions disable swap accounting by default because
of higher memory usage.
Nomad silently ignores if writing to the memsw.limit_in_bytes file
fails. The allocation succeeds, no message is logged to notify the
user.
To ensure that disabling swap works on common Linux kernels, disable
swapping by writing 0 to the memory.swappiness file.
Using the memory.swappiness file only requires that the kernel is
compiled with CONFIG_MEMCG=yes. This is the default in common Linux
kernels.
